Are Beavers Good or Bad for Trout Streams?

An angler in northern Wisconsin fishes above a beaver dam that blocks trout access, increases silting, and warms the coldwater habitat . Photo by Len Harris.

In his essay “Thinking like a Mountain” Aldo Leopold, hailed as the “father of
wildlife management,” describes a mountain rendered wolfless by humans:

“I have seen every edible bush and seedling browsed, first to anaemic desuetude, and then to death. I have seen every edible tree defoliated to the height of a saddlehorn. Such a mountain looks as if someone had given God a new pruning shears, and forbidden Him all other exercise. In the end the starved bones of the hoped-for deer herd, dead of its own too-much, bleach with the bones of the dead sage, or molder under the high-lined junipers.”

The broader lesson remains largely unlearned. A case in point is the inability of
most Americans to accept the realities of beaver overpopulation.

West vs East

The causes of ecological damage by overpopulated deer and beavers are identical.
Wolves, the major predators of both species, have been extirpated or severely
reduced in most deer and beaver range. And clear-cutting has replaced natural old-
growth habitat with deer and beaver candy such as aspen and willow.

Beavers in natural abundance are good for native ecosystems, salmonids included.
In much of the Pacific Northwest, beavers are depleted, and managers are rightly
attempting recovery.

According to Bill Bakke, founder of the Oregon-based Native Fish Society:

“Beavers got socked in the 1840s. Mainly it was the English trying to keep Americans from coming here for pelts. Hudson’s Bay Company sent out work parties to eliminate beavers. They haven’t fully recovered, and they’re still being trapped. We’re trying to get the agencies to recognize that beavers enhance both fish and water quality.”

“Beavers create reservoirs of cool water that salmon need to survive,” report the
Northwest Treaty Tribes of Western Washington State in a news release entitled
“Beavers Relocated to Improve Salmon Habitat.”

Such assertions are accurate in much of the West, at least where there are cold,
high-gradient streams. But when cited as evidence that all beavers everywhere in
all quantities are great for all species, they’re flat wrong. Do a Google search for
“beavers and trout,” and once you get past the excoriations of fisheries managers
who attempt to control a few gross beaver irruptions, all you’ll find are effusions
about how beavers fix whatever ails the earth.

For years the only leghold traps legal in my state of Massachusetts were water sets
that drowned beavers. But in 1996 voters approved a ballot initiative outlawing all
body-gripping traps, water sets included. I am no fan of drowning animals with
leghold traps and even less of a fan of trapping them with legholds on land. But by
the early 21 st century our beaver population had quadrupled, causing grave
ecological damage.

Since then, the state’s beavers have declined because they’ve stripped away so
much forage, but they’re still overpopulated. Benthic organisms such as aquatic
salamanders, mussels, crayfish, insects, and hibernating frogs and turtles (some
imperiled) freeze to death when beaver dams are ripped out by flooded property
owners. These days animal-control agents are called in to “humanely” remove
nuisance beavers. After the beavers are caught in folding wire-mesh traps that
immobilize and terrorize them all night they’re clubbed to death and usually land-
filled. We’ve converted a resource to a pest.

As in other states, the beaver overpopulation in Massachusetts resulted from wolf
extirpation and human-caused habitat manipulation. Trapping merely kept it
somewhat in check.

Now, in what were some of my favorite trout streams where I used to stand on
clean gravel catching wild brookies, I slog through scat-festooned silt, catching
fallfish or nothing.

A once free-flowing stream is now slower and warmer, allowing invasive trout to out-compete native brookies. Photo by Len Harris

Habitat Destruction

But beaver blight in the East is mild compared to that in the Midwest. Angler/photographer Len Harris of Richland Center, Wisconsin describes the pre-hangover high that comes with the discovery of a new beaver pond:

“It’s smile-producing at first because of bigger trout. But the flooding cycle cleans out that dam and all the barren bank. The streams widen and increase in temperature. . . . My home waters have warmed by at least four degrees in the last twenty years. This is from a combination of beavers not being kept in check and climate change.

Warmer water, resulting gill lice, and resulting competition from brown trout have
stacked the deck against the natives. Humans need to limit beaver expansion near
our brook trout streams.”

Wisconsin fisheries biologist Scott Braden weighs in with this: “We pay USDA’s
Wildlife Services to trap beavers and remove dams in trout streams that have been
badly compromised by beavers. We’ve seen great success on the few streams
we’ve targeted. We’d like to do more, but the price is so high we can’t.”

When I asked Braden for an example, he offered Beaver Creek and Buckhorn
Springs. “They were really beaten up by beavers,” he said. “There was some brook
trout reproduction in the headwaters. But trout couldn’t get downstream; they were
basically gone. All that was left were dark, sedimented backwater sloughs full of
lily pads. It was just terrible. We were walking through chest-deep muck. It really
gave you an idea of how much damage overpopulated beavers do. After Wildlife
Services trapped beavers and removed dams, that cold water started rushing
downstream and scoured out all that muck and debris, making lots of habitat.
Within two years there were just thousands of brook trout throughout the system.”

Outdoor and history writer Bob Willging breached beaver dams by hand and with
explosives when he supervised Wildlife Services’ District for Northern Wisconsin.

“The program really takes a very small percentage of beavers in the state,” he
explains. “Most northern Wisconsin trout streams are small, narrow and have a low
to moderate gradient, which means a beaver-dam system floods hundreds of acres
of low land, basically inundating the original stream channel. Consequently, dams
on these systems may have a much greater impact on flow than a dam in the West
where the gradient is much higher. So this very real impact on stream flow can
result in warmer water, increased siltation and turbidity and actual water chemistry
changes… Beavers are given free rein on eighty-five percent of Wisconsin’s ten
thousand miles of designated trout streams plus all Wisconsin’s lakes, ponds and
warmwater streams.”

In northern Minnesota, wolves have fully recovered, but beavers have gotten far
ahead of them, and with the unnatural overabundance of forage it appears they’ll
stay that way. Recreational beaver trapping used to help a little, but it essentially
ceased 15 years ago when pelt prices tanked.

“Forest management here is geared toward aspen, and the rotation is about forty
years,” reports Minnesota fisheries biologist Jeff Tillma. “That means there’s lots
of young aspen on the landscape, and that creates prime beaver habitat.

Also, there’s a lack of shade and large woody input in the streams. Wood isn’t allowed to get old. The downed trees are so small they don’t stay put. We’d like better coordination between forestry and fisheries for longer-lived, uneven-aged management. Our beaver management is small-scale because of the expense. We do only a handful of streams in each area, and we do them annually. If we stop for any length of time, beavers return. We’ve seen very encouraging results—more and larger brook trout.”

Paiute cutthroat trout, the rarest salmonid in North America, has been restored to 100 percent of its natural habitat. Photo by Bill Somer

Apples and Oranges

Citing accurate but irrelevant beaver data from the Pacific Northwest, opponents of
beaver control savage Midwest fisheries biologists and especially Wildlife Services
which, because of its predator control, they perceive as a surface extension of the
underworld.

Non-anglers rarely encounter fish. Fish are cold, slimy, unheard, unfeathered and
unfurred. So, for much of the public, including an element of the environmental
community, fish don’t count as wildlife. This is why opponents of beaver control
invariably proclaim that restoring brook trout, a species threatened in fact if not by
federal decree, is solely to sate angler appetites.

Herewith, two typical comments from websites:

“They kill and shitcan thousands of beavers and persistently drain wetlands to make it easier for duffers to fill their creels.” And: “The thought of how much damage is done culling beavers in the name of fishermen pisses me off.”

“Fish fervor destroys beavers,” shouts of piece entitled “Wisconsin’s War on
Nature” in Beaver Sprite magazine. “Since 1985 the Wisconsin Department of
Natural Resources has waged a successful campaign to wipe out 70 percent of the
state’s beavers for the declared benefit of trout fishermen.” (The department has
wiped out no such percentage. Maybe .05 percent and only briefly before
recruitment replaced the loss).

Among the loudest and most ecologically challenged decriers of trout recovery via
limited control of grossly overpopulated beavers is an outfit called Worth a Dam.
It’s based in California where beavers are generally not overpopulated and where,
because of the many cold, high-gradient streams, they do more good than harm.
One of the group’s nameless non-anglers posts as follows, scolding me for an old
op-ed:

“Maybe you could spend five minutes in an actual trout stream with an
actual beaver dam. Or hey, maybe snorkel in it and see all the baby trout swimming
around?” And this brazen untruth: “The Wisconsin DNR studies have shown that
beaver dams do not inhibit trout movement and they do not negatively effect [sic]
watershed stream temperatures.”

Before and after dam removal on a beaver-compromised, low-gradient trout stream in northern Wisconsin. Photo courtesy of Wisconsin DNR

Beaver-Control Battles

According to Willging:

“Unfortunately, coldwater systems are declining in the United States. And in many areas the sustainability of native book trout populations is in jeopardy. But coldwater-stream ecosystems are not just about brook trout. They are
rich in species diversity. For many unique species, including insects, mollusks,
crustaceans, amphibians and fish, they provide habitat and refuge from warm
water, flooding and predators.”

In the Duluth, Minnesota area a group called Advocates for the Knife River
Watershed is fighting beaver control on the Knife River system, citing all manner
of inapplicable studies from the Pacific Northwest and making such preposterous
claims as “Beavers have been totally eradicated in the whole Knife River Valley,
over 200 square miles.”

Even with beaver control there are far more beavers in the Knife system than
before Europeans arrived and one hell of a lot fewer native coaster brook trout
moving up from Lake Superior.

The Knife is among the state’s most important steelhead streams. Most of the work
on the Knife system is aimed at opening blocked steelhead spawning access.
Advocates for the Knife River Watershed charge that the DNR is sacrificing native
coasters for aliens. Does it have a point?

No, because DNR is “sacrificing” nothing. What’s good for steelhead is good for
coasters. Beavers are still way overpopulated in the watershed. And, while
steelhead are indeed alien to lake and tributaries, they are an important self-
sustaining resource adored by anglers and a boon to the state’s economy.
All the noise has prompted DNR to back off a bit. But some beaver control
continues. Duluth area fisheries supervisor Deserae Hendrickson offers this:

“Funding is extremely limited, so we’ve had to target fairly specific mainstem
areas in the Knife and Blackhoof-Nemadji watersheds that are critical for
migratory fish.”

While salmonids benefit from beavers in much of the West, beaver irruptions are
nuking coldwater habitat even there. In Nevada, as in Wisconsin, Minnesota and
Massachusetts, concerned citizens have proved they can make a difference.
They’ve proved also that this isn’t always a good thing.

To save imperiled trout, the Nevada Department of Wildlife was taking out a few
beavers until the 1990s, when concerned citizens whipped to a froth of pique by
the Humane Society of the United States, convinced politicians to shut down the
program.

The state hasn’t dared to step back into that fray since. But 13 years ago, Nevada
committed to restoring native trout in historic ranges—primarily federally
threatened Lahontan cutthroat, but also Bonneville and westslope cutthroat, bull
trout and redbands.

“When that push started,” reports the Department of Wildlife’s former conservation
educator, Kim Toulouse, “we discovered that many single-order streams were
infested with heavy beaver populations. Extremely high numbers of beaver dams
led to loss of gene flow and precluded the ability of fish to move up and down
these systems. Additionally, fish had difficulty finding suitable spawning grounds
due to heavy siltation caused by the dams. The loss of riparian habitat led to
erosion, more siltation, less shade, higher water temperatures, loss of native
riparian vegetation, and establishment of noxious invasive plants. In some cases,
increased sunlight has allowed establishment of nonnative submerged vegetation
like Eurasian milfoil.”

On Nevada’s Truckee River, the U.S. Fish and Wildlife Service is trying to recover
salmon-size Lahontans that migrate up from Pyramid Lake to spawn. Toulouse,
who lives within a half mile of the Truckee, fishes it regularly. It’s overrun with
beavers—bank dwellers because the mainstem is too big for dams. “On a number
of reaches, beavers have decimated the entire cottonwood population on both
banks,” Toulouse reports. “That has removed shade and insect populations,
primarily terrestrials. Replacing the cottonwoods have been mainly [nonnative]
invasives like tall whitetop. It’s very difficult to treat. It takes over everything, and
it releases a toxin that prevents the spread of natives.”

Fisheries Technician Lloyd Anderson after breaching a beaver dam on beaver-compromised Stoney Brook in Cass County, Minnesota. Photo by Fisheries Specialist Owen Baird, Minnesota DNR.

Bad Science

In California’s Silver King Creek in the Carson Iceberg Wilderness of the High
Sierras, the Paiute cutthroat trout was being hybridized off the planet by alien
rainbows. It would now be extinct had beaver dams been left in place.
The only tool to save this, the rarest North American salmonid, was the organic
piscicide rotenone. Genetically pure fish were available from an off-basin refuge
created in 1946 by the U.S. Forest Service in naturally fishless Cottonwood Creek
high in California’s White Mountains.

Rotenone, applied in running water at 50 parts per billion, is so short-lived that it
can lose toxicity in an hour. In modern fisheries management, it has never been
seen to permanently affect an aquatic ecosystem except to restore it. And it has
restored the entire ecosystem of Silver King Creek including Paiute cutthroats.
This is the only salmonid recovery project in the world that has returned a native
fish to 100 percent of its natural habitat.

But litigation and appeals from environmental groups and individuals calling
themselves environmentalists blocked Paiute recovery for a decade, costing the
recovery team (managers from the California Department of Fish and Wildlife, the
U.S. Forest Service and the U.S. Fish and Wildlife Service) hundreds of thousands
of dollars and nearly ushering the Paiute into oblivion.

Rotenone can’t affect air-breathing organisms. But opponents, for whom fish don’t
count as wildlife, argued that it would kill everything in or near the stream, beavers
included. They alleged that rotenone’s single purpose everywhere it’s deployed is
to benefit recreationists who, in this case, supposedly could not wait to hike 15
miles uphill into wilderness to catch 7-inch fish.

A few days after the 2015 rotenone treatment, beavers rebuilt the dams. That was
fine with the recovery team because of Silver King Creek’s icy flow and high
gradient.

But beavers had devastated Silver King’s lower-gradient tributary Four-Mile
Canyon Creek, a vital Paiute sanctuary. “The dams caused a lot of erosion up
there,” remarks former California Fish and Wildlife’s fisheries biologist Bill
Somer. “Trout Unlimited brought in volunteers and successively rerouted the
stream. The biggest problem I see with beavers is that after they move into an area
and eliminate forage, they abandon their dams. When these dams, which have
captured sediment, blow out there’s erosion. I’ve seen that in a lot of places.”

Wildlife Services explosives specialist prepares binary explosives for beaver dam removal on a beaver-compromised, low-gradient trout stream in northern Wisconsin. Photo courtesy of Wisconsin DNR.

Weighing Pros and Cons

Beavers are like red wine. Because one glass a day may be heart-healthy, one
should not conclude that 40 glasses a day are 40 times better, or better at all.
Wildlife advocates need to keep two different thoughts about beavers in their
brains simultaneously: 1. Beavers in natural abundance are good for coldwater
species. 2. Unnatural proliferation of beavers caused by human activity kills
coldwater species.

“Letting nature take its course” does not mean sitting on our hands after we’ve
disrupted nature.

Aldo Leopold was a trout fisherman. Were he alive today, he’d advocate for beaver
recovery and beaver control where each is needed. And he’d salute angler, former
guide and now Midcurrent editor Phil Monahan, who wrote this in Trout
Unlimited’s Trout Magazine:

“Many anglers see the beavers’ work as predominately destructive—turning a babbling trout stream into a slow-moving wetland, for instance. Wildlife biologists recognize that each of these ‘destructive’ effects has a flip side: situations in which that very same effect is beneficial to trout. “After looking at all the data, then, the question, ‘Are beavers good or bad for trout streams?’ can be answered only with a definitive: ‘It depends.’”

It’s unlikely that managers will ever be able to restore more than a tiny fraction of
trout streams destroyed by overpopulated beavers. But as Leopold wrote in a 1946
letter to his friend Bill Vogt:

“That [a] situation appears hopeless should not prevent us from doing our best.”

Ted Williams, a former information officer for the Massachusetts Division of
Fisheries and Wildlife, writes exclusively about fish and wildlife.