A Balanced Perspective On Small Scale Dredging


A balanced perspective on small scale dredging.

There is an old adage that says, “If you shout something loud enough, long enough, and often enough……it becomes believable enough, by enough people….to pass as fact.”

Thus is the hope of environmentalists who claim that small scale dredging is harmful to fish.  Environmentalists and other special-interest groups have recently been engaged in an all-out assault against small scale dredgers, alleging that this mining activity is harming fish.  Well, actually, what they are saying is that this activity “may” harm fish, and on that basis alone, they are seeking to shut down the small scale dredging industry.  Their allegations are rife with supposition such as “may”, “could”, “might”, “can”, etc.  Now, there’s a good reason for this.

Generally, when someone is alleged to be causing environmental harm, there are two things.  First of all, there is scientific evidence that environmental harm is being caused in the first place….a corpse if you will….a dead herd of buffalo, dead birds laying on the ground, defective eggs, mutant lizards, or in this case, dead or injured fish.  Secondly, there is sound scientific proof that a particular activity or situation is causing this harm.  Ironically, in the issue of small scale dredging, neither of these two factors is present.  Neither environmentalists nor biologists who have monitored small scale dredging for decades have provided any scientific proof whatsoever that a small scale dredger has ever harmed a single fish!  Let me repeat that.

Not… one… single… fish!

Yet, they continue to press their assault against small scale dredgers, seeking a political solution while circumventing scientific discovery and the public review process in an effort that is completely devoid of a single fragment of proof.  The fact is, that small scale dredgers actually help the fish in a number of very important ways.

Let us understand something here.  Environmentalism is a wonderful thing.  It has driven the cleanup of many of our rivers and harbors.  It has exposed many pollution sites, and placed the responsibility for cleanup of these sites squarely in the laps of those responsible.  And it has fostered protection for endangered species.  Unfortunately, as with all good things, there are those who would abuse it.  In addition to its great accomplishments, environmentalism has become a powerful and convenient tool for many “NIMBY“ (not in my back yard) activists.    Many of the involvements by environmentalists were not born of concern for the environment, but by political agenda.  Opponents of an unwanted presence can challenge this presence with a powerful tool while cloaking themselves in righteous deed.  The Endangered Species Act (ESA) which they frequently rely upon has virtually become the preeminent law of our nation, it is so powerful.  Environmental laws, as presently written, often permit a small, radical-thinking, agenda-driven, and often misinformed minority to impose their philosophies upon the general masses with little accountability.  And, we as human beings often find such power too seductive to sensibly meter.  I am a dredger and an environmentally-conscious person.  I admire environmentalists for the good that they do, but I cannot admire their sometimes misdirection, and their prostitution of environmental laws as a political tool.

First of all, it is highly obvious that environmentalists and their legal advocates generally know very little about dredging for gold or they would not make some of the outlandish claims that they do.  They are largely unfamiliar with the scope and mechanics of a small scale dredge operation and apparently are hoping that the courts in which they plead their cause are equally unaware as well.

It is important to first understand how a dredge works.


A dredge is a small mechanical platform that is mounted on floats.  It consists of a small engine, a water pump, an inclined sluice ramp, and sometimes an air compressor to enable the dredger to breathe underwater.  A suction hose is attached to the front of the dredge.  Water is propelled through this hose by an injection of water from the water pump.  This pumped water is injected up the dredge hose at a very shallow angle, and thereby causes greater volumes of water to be propelled up the dredge hose by what is known as the “venturi principle”.  None of the dredged water or material passes through any pump or mechanical device.  The dredged material enters the front of the dredge, where it spreads out, slows down, and flows down over a series of small barriers known as “riffles”, and then out the back of the dredge.  This section of the dredge is known as the “sluice”.  It is now important to understand that gold is just about the heaviest thing found in a stream.  Gold has a “relative weight” of 19.  (Water has a “relative weight” of 1.)  Therefore, gold is 19 times as heavy as water of equal volume.

Dredged water and streambed materials easily travel down this sluice mechanism and out the back of the dredge.  Because gold is so heavy, it will drop out of the material flow and become lodged in these “riffles”.  This is how miners capture the gold and not everything else.  Other things that are relatively heavy, though not as heavy as gold, will also become lodged in the sluice.  This includes “black sand” which contains quantities of iron, fishing lures, tools, lead sinkers, gunshot, beer-can tabs, and just about any other form of metal junk that is unearthed by the dredge.  Also, another very heavy element, poisonous mercury from ancient mining methods and other industrial contributors is often captured in a dredge and can now be safely disposed of.  As you can see, a dredge is somewhat of a “vacuum cleaner” and in addition to capturing gold can help significantly to remove many pollutants from a streambed.


Compared to the natural lay of a stream, dredging activity is quite insignificant.  Even in the most heavily dredged regions the area affected by dredging is almost always less than even one percent of the area of a waterway.  This has been established by surveys.  A dredger who moves a single cubic yard of material has done a very hard day’s work.    A typical dredger will usually be accomplishing “productive work” between two and four hours a day in the stream.  And, due to the exhaustive nature of the activity, along with things such as weather considerations, a dredger will seldom work every day.

The typical dredging operation involves working a hole down through the streambed material until they reach solid bedrock where gold, being the heaviest thing in the stream, has settled.  Gold, as well as all other streambed material is moved downstream by raging winter floods.  This gold will readily become lodged in cracks and crevices in the bedrock.  It is primarily these imperfections in the bedrock that the dredger is looking for.  There are particular areas of a stream or river where gold is most likely to be found but it is still mostly a matter of chance.

Having provided a basic understanding of a small scale dredging operation, we can now examine some of the claims made by opponents of small scale dredging.  These claims have been numerous and are mostly without scientific foundation.  Once the allegations are proven false, they simply move on to a different allegation.


Actually, the opposite is true.  In a dredge hole six feet wide by six feet deep it is not uncommon to see over a dozen juvenile fish in the hole in close proximity to the operator.  They are usually looking for edible tidbits that are unearthed by the dredger or they have ducked into the hole to rest from the currents.  The motor on a dredge is almost not audible underwater.  Many times, the only way that a dredger knows that his/her engine has run out of gas is by the fact that their air supply quits and the dredge hose stops suctioning.  This requires a mad scramble to the surface.  The most prominent sound when operating a dredge is a “whooshing” sound made by aggregates going up the dredge hose.  This is much like the normal rushing sound that you will hear underwater in any stream.  Fish are normally spooked only by fast-moving, ominous objects such as a kayak, canoe, or other watercraft, swimmers or waders, or an obvious predator.


This claim is completely false.  First of all, the only thing that is warm or hot on a dredge is the engine.  Absolutely no water comes in contact with the air-cooled motor or its hot exhaust.  Dredges are not like outboard motors where the hot (and oily) exhaust is vented underwater and the engine is cooled by water.  If a dredge has any effect on the temperature of water at all it probably cools it slightly due to the aeration and evaporation of the water as it flows over the riffles of the sluice.  Scientists have measured water temperatures of numerous streams and rivers above and below a dredge and were unable to measure any difference whatsoever.


Of course it does.  Any activity in a stream creates turbidity whether it be a fisherman wading in a stream, animals walking in the stream, a group of children frolicking in their favorite swimming hole, or a tree or rock falling into the stream.  The important concerns are how severe the turbidity is, how widespread it is, and how prolonged it is.

To get some idea of the level of turbidity that is usually created by a dredge we must understand some facts about dredging.  A dredger cannot operate in water where there is an appreciable level of turbidity at all.  When visibility is impaired, dredgers cannot see what they are doing.   They cannot see the gold that is trapped in crevices, and rocks that are overly large will get suctioned by the dredge nozzle and plug the dredge hose.  These plug-ups are very difficult to remove.  In addition, dredgers cannot see the looming danger of boulders that could tumble in on them and injure or kill them.

It is common for dredgers to set up within 50 or 100 feet downstream of each other with no visibility problems, yet events such as dam releases or thunderstorms will cause the level of turbidity in the entire river to rise to the level that dredgers have to abandon their activity for several days.  Even within the area of a normal dredge plume the level of turbidity is only a tiny fraction of what is created by naturally-occurring and long-enduring events such as storms and winter floods which fish routinely endure.  One single thunderstorm creates many times the turbidity in a given river or stream than is created by all dredging activity for an entire year.

Additionally, biologists have noted that juvenile fish will seek refuge in a plume of turbidity when they feel threatened.  Scientists have observed that these fish swim and feed noticeably more in an area of more turbid water.


Absolutely false.  A dredge adds nothing whatsoever to the waterway.  The material that comes out the back of a dredge is the very same material that was lying on the bottom of the waterway.  It has simply been moved a few feet.  However, as mentioned previously, a dredge does remove many pollutants from a waterway.  While we are on the subject of pollution, this would be a good time to discuss one of the most lethal pollutants in a waterway….. mercury.  Mercury is a very heavy, highly toxic metal that exists in a liquid state and usually concentrates in “blobs” in any depression.  Mercury will readily adhere to gold and various other metals and coat them.  It will also cause small particles of these metals to bind together, much like the fillings that dentists put in our teeth.

One of the greatest concerns with toxic mercury is its ability to enter the food chain, such as in fish.  It does not do this as a blob but rather as microscopic particles.  When mercury is sitting in a waterway, disturbances and agitation such as tumbling boulders smashing this blob, or gravels scouring this blob, can cause a few microscopic particles to break away and become mobilized in the waterway.  This is known as “flouring”.  As long as this blob remains in the waterway, it is prone to flouring from constant disturbance until it flours away completely and becomes a toxic poison to many living organisms.  The only way to stop this contamination is to remove these blobs of mercury and other mercury coated metals from the waterway.  This is exactly what a small scale dredger does!

A recent experiment done by the state of California showed that a small scale dredge captured 98% of this toxic mercury from a waterway.  It should be noted that this experiment was conducted by an inexperienced operator using an obsolete “crash box” type of dredge.  Miners widely feel that if this experiment had been conducted by an experienced dredger using a modern “jet flare” dredge, the recovery would have been close to, if not 100 percent.  California then concluded that it would be best to leave all of this mercury laying in the streambed rather than risk the remobilization of the 2 percent that they allege escaped the dredge!  They claim that the mercury is safely immobilized deep in the streambed material.

Every dredger on the planet knows that this assumption is absolutely ridiculous.  Many, if not most streams and rivers are scoured right down to bedrock during the most severe flood events.  (Someone has obviously never visited the Grand Canyon).  Small scale dredging is the only economically viable way to remove this poisonous mercury from our waterways.  Gold dredgers do this at absolutely no taxpayer expense in their search for gold.


Absolutely false.  Dredging is not allowed until well outside of the spawning season.

These are just a few of the marathon claims that environmentalists have alleged against dredgers, but they are among the most important.  Now, let’s look at the other side of the coin.  I previously mentioned that dredgers provide several benefits to fish.  They do, and they are very important to the survival of fish and will be discussed in detail.  Most of the discussion will be as it pertains to salmon, as it is this species that is at the heart of the present controversy.  When a dredger searches for gold in a stream he/she basically creates three alterations to the streambed.  These alterations are…..the dredge hole, a tailing pile, and a cobble pile.


Environmentalists do not generally give a lot of lip service to the dredge hole itself aside from the fact that it can be considered a challenge for persons wading in a rocky stream.  Some even acknowledge that the dredge hole can have a benefit for fish.  The annual spawning migration is a very strenuous trip for fish and there can be a significant mortality of fish during this migration.  The fish become weakened by their constant struggle against strong water currents.  Also important is the fact that fish migrate during the time of year when the water is near its warmest.  Warmer water contains less oxygen, heightens the chance of disease, and saps the strength of fish.  Fish will often pause in an area of river where a cooler side-stream enters the river to regain their strength.  These areas are known as thermal refuges.  Dredging is often prohibited within a certain distance of these refuges.  In between these natural refuges, migrating fish will frequently duck into vacant dredge holes where the water is calm and the temperature is stratified with the cooler water being near the bottom.  Frequently, a dozen or more adult fish can be observed using dredge holes. In many instances, fish seem to prefer dredge holes over natural refuges, possibly due to the depth and calm water.

Prior to the migration season, these dredge holes are extremely important to juvenile fish.  As the summer wears on and water levels drop, predation of these small fish by birds and mammals increases immensely.  It is at this time that these smaller fish seek shelter in deeper pools if they can find them.  These dredge holes are an ideal refuge.


These are the piles of gravel-like aggregates that come out the back of a dredge.  These tailing piles are also one of the present focuses of mining opponents who are desperately searching for a valid indictment of small-scale dredging.  Many people are of the flawed assumption that a streambed is a stable environment.  This is incorrect.  A riverine environment is constantly being “rebuilt” by natural hydraulic forces.  Streambed composition varies from place to place and from year to year.

When salmon spawn in the late fall, they try to select a streambed area that is shallow, relatively flat, free of fast currents, and comprised of loose gravel in which they can lay and bury their eggs.  However, fish are so driven by nature’s call that they will spawn even if they cannot find a suitable site.  Unfortunately, in this case their eggs are less likely to survive.  Once fish lay their eggs, these sites are known as (redds).

Since the composition of tailing piles is sometimes similar to the loose, gravely material that spawning fish prefer, they occasionally select a tailing pile as their spawning site.  The extent to which fish select tailing piles is dependant upon the availability of natural beds.  A recent biological study in Northern California found that out of a total of 372 “redds”, 12 of them, or roughly 3 percent were on tailing piles.  Elsewhere, it has been observed that when natural beds are scarce, the selection of tailing piles increases.  In rare instances where spawning fish have entered streams in which the streambed has become compacted or silted-over and there are no natural beds available, tailing piles offer virtually the only suitable opportunity to successfully spawn.

There are two primary concerns with regard to the survival rates of the eggs within these redds….scouring and siltation.  Scouring occurs when the unstable material of a streambed is moved downstream.  This movement is usually greatest during the winter floods.  Siltation, or the covering of redds by silt, is of far more concern than scouring.  Although the extent of mortality by scouring is not of a known quantity, mortality by siltation is often complete as the eggs and pre-emergent fish become smothered by silt.  Some biologists have even suggested that a certain amount of scouring is actually desirable to limit silting in some of these spawning beds.

Due to the fact that some of the newly created tailing piles may not have had the opportunity to go through a flood event and become flattened and stabilized, there is a potential for more movement and scouring in these piles than there would be in a natural streambed spawning site.  This might possibly result in greater mortality for eggs that were laid in fresh tailing piles.  It has been noted, however, that once these tailing piles have become flattened and stabilized by winter floods, they can remain viable as a suitable spawning site for a period of several years.  This is extremely important in streams where there are few or no natural sites available.  Even during the first winter when scouring would likely be at its greatest, these tailing piles afford at least some opportunity to successfully spawn in a stream that might otherwise provide none.  Also, these stabilized tailing piles likely are less susceptible to silting and scouring than natural streambed due to the fact that once they are flattened and stabilized these tailing piles generally remain slightly elevated above the surrounding streambed.  And, these tailing piles start out as washed streambed material, therefore they are free of silt in the first place.  It is not known how many of the “natural beds” that were counted in this study were actually former tailing piles that had become flattened.

In view of the fact that fish tend to select tailing piles very infrequently, and only as necessary, and that stabilized tailing piles can provide prolonged spawning opportunity where there would otherwise be little or none, it would seem only logical that the known benefits of this relationship far outweigh any possible harm.  We must also keep in mind the fact that scouring in a streambed is not “selective” only to fresh tailing piles.  The entire streambed is vulnerable to scouring during raging winter floods.


These are rocks that will not pass through the dredge hose and consequently are piled to one side by the dredger.  They usually range in size from roughly 12 inches in diameter down to about 3 inches, depending upon the size of the dredge.  Larger than this, the rocks are generally too heavy to pile.  These piles represent a certain percentage of the aggregate removed from a dredge hole. About the most frequent claim by mining opponents is that these piles may divert the flow of water and may “possibly” cause erosion of river banks.  At this point in time it would seem proper to mention that dredging into riverbanks, undercutting riverbanks, and doing anything that would cause erosion of riverbanks is strictly forbidden by dredging regulations.  Dredging operations are frequently monitored by enforcement personnel.  Dredging is a tightly regulated and monitored activity.

Secondly, dredging is usually not done adjacent to riverbanks, but closer to the deepest part of the stream or river as this is where the gold has settled.  In those places where the deepest channel is along the side of a river or stream, the bank is usually not composed of soil but rather by ledge or gravels.  The soil was eroded away eons ago by the natural river currents.

Additionally, dredgers do not begin their activity until the time of year when the flow is the slowest, the water level is the lowest, and any hydraulic forces are at their minimum.

It is hard to imagine that a pile of rocks resting on the bottom of a stream or river could provide very much benefit to anyone or anything, but it does.  And this one is quite important.

Salmon generally spawn in the late fall in favorable gravel beds that they select as best they can.  After a period of incubation, the small fish (fry) emerge from these gravels during the spring months.  Immediately after emerging, these fish are very small, they are relatively poor swimmers, and it is during this time that they are in great danger of predation.  Fish lay eggs by the billions but only a very small fraction of them ever survive to adulthood.  The juvenile stage is a period of very heavy losses.  It is infinitely important that juvenile fish are able to find shelter from predation during this stage of their growth.  This is where cobble piles come into the picture.  Cobble piles provide an excellent refuge for these small fish.  Fish of various sizes hide throughout these piles.  Biologists widely acknowledge the importance of “streambed diversity,” and “structural complexity” to the survival and well-being of fish.  Furthermore, these artificial habitats are comprised of natural materials, unlike in our oceans where these habitats are created by the intentional sinking of rusting, painted, and oily derelict ships.


There are a couple other benefits that dredgers provide that I will mention.  One of them is rather insignificant and the other is quite important.  During the fall migration of spawning adults, the water is warm and holds less dissolved oxygen (DO).  There is pressure on the oxygen content by the struggling dwellers that live there.   Dredges force voluminous amounts of water down over the sluice section, mixing this water with air and this helps to aerate the water and increase the oxygen content.  This is a small amount compared to natural rapids, but every little bit helps.

One other benefit that is provided by dredgers is extremely important.  Fish often swarm around an operating dredge like pigeons around a popcorn stand.  They swim into the dredge hole as well as swimming through the dredge plume.  They are there because as a dredger suctions streambed material, he/she unearths thousands of invertebrates and suspends them in the water, and like any wild creature, these fish are drawn to food.  Finding adequate food is one of the most important aspects in the life of a juvenile fish.  The better the fish are fed, the more likely they are to survive, due to healthy growth and a diminishing predator pool.  Scientists have also observed a direct  correlation between the amount of time juvenile fish spend foraging and their susceptibility to predation.  The faster the fish can feed, and then hide, the better off they are.  When food is scarce, predation increases.

It does not take a genius to question the fact that when fish are being fed grain in a hatchery, it is considered an ultimate act of conservation, yet when native fish are feasting on their natural diet in the plume of a dredge it is somehow biologically unimportant.  A dredger who spends a couple months in a given section of a river has provided a lot of food to the native fish population.  Incidentally, biologists have observed that these invertebrates rapidly re-colonize, usually within three to four weeks.

Native, juvenile, and migrating fish must find sufficient food, shelter from predation, reprieve from harsh temperatures, a place to rest from swift currents during their exhausting migration, and suitable spawning habitat.  Small scale dredging provides all of these.  And, dredgers are the only waterway users who provide any of these important benefits that the fish so greatly need.  It is almost unimaginable to me that environmentalists who are attacking dredgers aren’t the real friends of fish at all.  If the environmentalists were honestly concerned about fish and really wanted to do something to help them, instead of sitting around and suing everybody, they would get up off their fannies, jump in the water, dig pools, pile cobble for refuges, provide food, and spread out gravel for spawning beds in our streams….just like the dredgers do with their sweat, back, and labor.  Dredgers not only do this without any expense to the taxpayers, but dredgers actually pay hefty permit fees for this opportunity.  Conversely as this essay is being written, our government is spending millions of taxpayer dollars to, among other things, spread out countless tons of gravel for spawning habitat in the Trinity River in California.  Incidentally, you wouldn’t believe the staggering amount of turbidity that is being created by the behemoth earthmoving machines that are being used for that project.

And some of the most avid accusers of dredgers are Indian tribes who sometimes “front” for environmental groups, and accuse dredgers of causing harm (without any proof) while their tribal members net and harvest spawning adult salmon by the thousands as these fish are returning to their spawning grounds!!!  I can think of a way to help these fish………right now!!

Dredging is a very visible form of mining.  Dredgers do not crawl into a hole in the side of a mountain.  They do not dig in a pit that is surrounded by a privacy fence.  Their activity is out there for all to see.  One can usually look down onto a river and see their dredges floating on the water.  There is sometimes a visible plume trailing downstream from them.  One can hear the distant drone of a lawnmower-sized engine, and if the stream is exceptionally clear one can sometimes see the dredge hole and cobble pile that are underwater.  Dredgers frequently park vehicles beside a roadway, near to where they are working.  To some, this intrusion into nature is disturbing.  However, at the same time, dredging is perhaps the most reversible form of gold mining that there is.  Virtually all traces of dredging activity are obliterated by the winter floods that occur after each dredging season  The dredge hole is completely filled in, the cobble pile is leveled, and the tailing pile is flattened and spread out, offering itself as a potential spawning site for years to come.

When examining environmental issues and trying to decide the proper course of action, we must carefully consider all of the important factors, not just the ones that suit our purpose.

It is reasonable to expect that as members of our scientific community, biologists would be completely neutral in their approach and in their findings, and that their opinions would be all-encompassing and free of political influence.  It is also reasonable to expect that their opinions are based on empirical data gathered through honest observation.  This has not happened.

Several biologists have chimed in on the dredging issue.  Many of these biologists have never even observed a dredging operation, and don’t seem eager to do so, in spite of numerous invitations from dredgers to go “down below” and observe first-hand.  Yet some of these biologists render opinions critical of dredging.  Some of them simply cite “cherry picked” segments of studies done by others.  Some of them suggest the hypothetical “possibility” of harm while minimizing or omitting potential or known benefits.  Some of these opinions are based upon scientifically unproven assumptions!  Assumptions!!  This isn’t balanced science!  Hey, if you are going to render a “scientific” opinion that could destroy thousands of people’s livelihoods, and cost the economy tens of millions of dollars…..do some honest research!!

Now, there are several scientists with spot-on credentials who are actually very knowledgeable about dredging and its effects, because in addition to being career scientists, they just happen to also be experienced dredgers.  They know fully well the extent to which dredgers contribute to the wellbeing of fish.  They know fully well that dredgers provide very important benefits to fish at just the right time of year when they are most needed by the fish, and then these alterations are completely obliterated by raging winter floods.  They know fully well that the turbidity created by dredgers is a mere drop in a bucket compared to the millions of tons of mud, rocks, refrigerators, trees, stumps, truck tires, sewage, road oil, and other debris that are washed down our waterways during raging winter floods or a single thunderstorm for that matter, which fish routinely endure every year.

They know that small scale dredgers are “occasional users” of our waterways, no more so than fishermen, boaters, swimmers, or the seasonal kayak and rafting outfitters who organize daily trips down our waterways involving hundreds of participants who picnic, swim, bathe, relieve themselves, and camp overnight on the shores of these waterways.  And, unlike the highly regulated dredgers, these other waterway users are allowed to trample around in the waterway during a time when there are still incubating egg nests in the gravels!

Unfortunately, the opinions of these career scientists who are intimately knowledgeable about all aspects of dredging and its effects are being summarily ignored by authorities in a pre-ordained political agenda that small scale dredging must be regulated out of existence.

So let’s be honest here, shall we?  This debate isn’t about the environment, it’s about control, money, and politics.  The environment is simply the vehicle.  While dredgers are being targeted for extinction, even though there is no scientific evidence that they have ever harmed a single fish, the real killers of millions of fish and their eggs…Indian tribes, fishermen, recreationalists, and especially “jet boats” are given a free pass.   There is an old saying that says, “When you are a hammer, the whole world looks like a nail.”  Environmentalists, even when ill informed, will fight any and all battles in their efforts to establish themselves as the sole stewards of our public lands which belong to all of us, not just a self-appointed few who enrich themselves through environmental litigation.  It is infinitely important that these public lands be set aside and remain equally accessible for the enjoyment and reasonable use by all of our citizens.  We must cherish and sensibly safeguard these privileges, lest one day we no longer have them.

Many scientific papers and biological studies as well as personal experience were used in the preparation of this essay.  These studies and papers are readily available on the internet.  Thank you for taking the time to read this.


Harley L. Mullen

Leave a Reply