Brook Trout and Beaver Dams

Vandermark Creek is a trout stream feeding the upper Genesee River in western New York. I have fished the headwater section of the creek occasionally over a period of many years, particularly for native brook trout in the area of the Vandermark State Forest. The upper creek is surrounded by a mix of woodland and aging fields and has remained basically stable for as long as I have known it. Over the past 10 years, however, I’ve seen a marked decline in its brook trout numbers, and I have a theory as to why.

I don’t know when beaver came to be employed at the state forest, but the rodent engineers are there, and they’re rocking the ecology of the woods. So what, you may be thinking. Aren’t there bigger threats to native trout today, say hydro-fracking, silt accumulation, global warming, etcetera? Why worry about a mammal that’s evolved with brook trout over the eons? Granted, the eastern char has a lot to be concerned about today, but let’s not disregard the beaver.

Castor canadensis may have evolved naturally with brook trout on a multitude of eastern streams, but remember, the trout’s current range is a mere fraction of what it was in pre-colonial days, and the presence of expanding beaver colonies on a single brook trout water can have a major impact, especially if poor land use by our own two-legged species has already minimized the number of fish.

My introduction to Vandermark Creek came long ago, during my Alfred University days in the 1970s. Since then I’ve never caught more than two trout at a single outing there, and I’ve never fished downstream for the brown trout that are stocked on a minimal basis every year. The creek has never seemed all that good for fishing, though I did manage to land a nice 11-inch brookie on the stream about five years ago. My last two outings at the creek were unsuccessful, and on a recent winter morning I inspected the low, clear waters and saw little more than beaver dams, silt, and large quantities of chubs.

As the value of beaver fur has lessened over the past few decades, minimizing trapper interest, beaver populations have surged in many rural areas. The Avery Report, a study published in 1992, collected data from the impact of beaver colonies on trout streams in Wisconsin. The report had studied fish and mammal numbers before and after the removal of beaver dams on trout streams. After looking at streams for six years following the removal of beaver dams, the Avery Report concluded that brook trout numbers rose and that water temperatures cooled. Stream turbidity was reduced; gravel beds were again exposed, allowing the spawning process. The flow rate of streams increased; the depth of water and the channel widths decreased. Unfortunately, across the study area in the 1980s, summer air temperatures were higher than normal, thus the water temperatures of the streams were cooler by a mere 2 degrees Celsius. Considering the potential effect of global warming on native trout stream waters, conclusions from the studies of dam removal do not sound encouraging. As one report suggested, “air temperature is the most important element in controlling trout habitat.”

I saw many little beaver dams in various conditions along the creek, and though I briefly fantasized that the beavers could be discouraged and the beaver dams removed by hand, I also realized I’d need an army of assistance and I wasn’t even comfortable with the idea of messing around with nature, as unbalanced as it seemed in this location. It would be nice to see the sediment cleared away and to know that oxygen levels would be increased, but it would also be nice to see the whole human world living together in peace and harmony. It wasn’t going to happen any time soon.

It’s a different story in our western states. For example, beaver ponds in the Rocky Mountains often have an opposite effect on trout. The ponds allow herbaceous plants to grow, eventually adding to the food supply. But here we’re talking about water temperatures rising from the 40s into the 50s under harsh conditions, rather than rising from the 50s or 60s into the 70s or beyond. Western ponds tend to have short life spans for fishing opportunities, but some of the fastest brook trout fishing I ever experienced was on the beaver ponds of the Colorado Rockies.

I asked Scott Cornett, fisheries biologist for the Department of Environmental Conservation in western New York, to weigh in on the subject of beaver ponds on eastern trout streams, and Cornett replied, in part: “Most of our streams have become marginal temperature-wise for brookies due to our poor land use practices, and the beaver ponds just push them over the edge.” He went on to say that new beaver ponds occasionally allow good brook trout fishing, but they quickly become silted in. As beavers rapidly consume the nearby wood supply, the waters warm up to allow, at best, the spread of brown trout in the watershed.

I don’t know what can be done about the problem, if anything, other than encouraging good land use practices. I’d like to hear about your own experiences with brook trout at the beaver ponds, or your thoughts about the interesting rodent and the colorful char.

About rivertoprambles

Welcome to Rivertop Rambles. This is my blog about the headwaters country-far afield or close to home. I've been a fly-fisher, birder, and naturalist for most of my adult life. I've also written poetry and natural history books for thirty years. In Rambles I will mostly reflect on the backcountry of my Allegheny foothills in the northern tier of Pennsylvania and the southern tier of New York State. Sometimes I'll write about the wilderness in distant states, or of the wild places in the human soul. Other times I'll just reflect on the domestic life outdoors. In any case, I hope you enjoy. Let's ramble!
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16 Responses to Brook Trout and Beaver Dams

  1. Alan says:

    I’ve seen the same thing happen on a small stream I fish.
    More bullets for the brook trout to dodge.

  2. River Mud says:

    Beaver and brook trout co-existed wonderfully as far south as the Virginia coastal plain just a few hundred years ago. Alas, we’ve done everything we can to destroy the watersheds since then, including removing the beavers’ few predators.

    I understand the “oh no, silt” reaction, but honestly, if it’s not trapped behind a dam (of beaver or human construction), it’s going to be trapped somewhere else, probably in a high quality trout hole downstream. It doesn’t just magically vanish downstream.

    I can’t judge anybody else’s opinion on this one, because I’ve found myself on both sides of these arguments in the past – where the discussion is how (or whether) to control the factor that impacts 5% of the resource problem. Trying to “fish out” browns isn’t going to bring back brookies, especially in the northeast. Killing all beavers isn’t going to do it. Making better decisions about road runoff and land use might help. Might. That’s 95% of the problem.

  3. Quill Gordon says:

    The water in a beaver pond does slow down and warm up, making it less than ideal for brook trout, but when we start making judgements as to whether it’s a good thing or a bad thing, we do so from our human perspective. Leaving the effects of human development and “management” practices out of the equation, beavers have been damming streams and affecting brook trout for a lot longer than we’ve been around, so I have a hard time passing judgement on it.

    We look at things here and now, forgetting that while the brookies may “disappear” after a few seasons, the pond will eventually silt in and the stream will flow through a meadow and the brookies will reappear. Shrubs and trees will regrow, providing shade and protective cover, and no one will ever know a beaver pond was even there. But that takes generations and we have no patience for that. We want to catch fish and we want to catch them now, so we take it out on the beavers and stock fish more tolerant of conditions as they exist. Personally, I see the stocking of brown trout in former brookie waters as giving up. Either that, or just not being able to leave well enough alone.

    I trap beavers around Fish in a Barrel Pond to keep them out of my culverts and to preserve the levels of our flood control spillways. I also trap in the drainage above the lake, where there are no roads or development to throw things out of whack. One meadow I work is a 50-acre jumble of beaver dams and former ponds that have come and gone for hundreds of years. The brookies are doing just fine up there.

    I have a responsibility to protect our man-made structures and I don’t fret too much about instituting immediate and permanent reductions to the beaver work force when they move in, but no one will ever convince me that the beavers “ruined” a brook trout stream. We simply lack the vision to see the changes as part of a never ending cycle and that the whole of nature is against us when we try to keep things just the way they are or force them to be the way we would like to see them. Taking the long view does not seem to be a part of Human nature.

    Beavers are not a real, permanent, threat to brook trout. We are.

  4. Quill, and River Mud,
    Thank you for the thoughts. I agree wholeheartedly with the premise of the “long view” and the real threat to brook trout being us alone. The imbalance of nature that I spoke of is due to humankind, and not the beaver’s fault. We’ve killed off its predators, abused the lands and waters so what we see is shrinking territory for native trout. You may live in an area where habitats are preserved and where the trout may reappear after the ponds shift or disappear. My point is this: at Vandermark Creek (not uncommon in the Northeast) the effects of human use/abuse of the environment are never far away. Brookies may never have a chance to resurge in this water, not until we reevaluate what we’re doing on the land or else until we’re all dust in the wind, if then. Beavers don’t enter and “ruin” the stream; it’s already compromised. But warming waters may push it over the edge, another stream down. Count the streams in your watershed containing brook trout today, and then compare the number with the number it had 50 years ago, 100 years ago… The stream in front of my house had brookies in it 40 years ago, but nothing since. I plant willows along the banks, but until the highway department stops screwing around with the road and streambanks, there’s little hope.

    • River Mud says:

      Well, where I’ve lived (eastern MD, eastern VA, SW VA, and Western NC) the pattern you mention is dead on – except for the dates. Things are unstable for eastern brookies (especially if stocking were eliminated) but in many areas the # of streams containing them bottomed out 150 years ago, before state-sponsored stocking was a common practice. That a few of these streams and populations/sub populations are improving is great (and a testament to human intelligence), and that even more are “no longer in a steep decline” is grea toot, and (to your point) shows the impact of taking away some (any!!!) of the stresses on the fish.

      But to your point again, human activity holds such a heavy sword over these special places that you never quite know what is going to happen with the next highway, forestry, or development project upstream. And giving the “all clear” sign and hoping for the best is most assuredly a foolhardy gesture.

      And there’s nothing wrong with making decisions about human infrastructure (i.e. roads that EMS uses to access rural areas) vs. beavers. Our reality just behooves us to make conscious, well-educated decisions before we act. We (as a society) seem to be starting to show that trend. Won’t hold my breath though – the next “PROTECT EVERYTHING!” or “PROTECT NOTHING!!!” are just an election away….sigh.

      • River Mud says:

        “grea toot?”


      • River Mud, I guess I can only really comment on my rivertop region of PA/NY, and for that I’m referring to the numbers of wild brook trout streams with self-sustaining populations. Stocked waters are a whole other kettle of fish. They’re everywhere around here, and I’m thankful for them when I can’t fish for wild ones. Streams with wild populations unadulterated by stocked fish and not yet dominated by browns or rainbows are my subject here. Meanwhile we try to help nature heal some waters by planting trees, providing instream structures, TU/Soil & Water projects… and hope that the gas drilling boom doesn’t open up a field upstream when we’re finished. Walt


  5. River Mud says:

    I try not to think about the gas drilling. What a “potentially good thing turned into a debacle.” One of the things that fascinates me about human history is the very dimorphic (right word?) trends in natural resource use/mis-use in different regions (even within the USA) over time. It’s actually conceivable that by the first time the Northeast’s interior was heavily deforested for the first time (mid 1800s), American foresters had actually learned something from deforesting the entire coastal plain and piedmont from north Florida to Maine (early 1700s). Hey, it’s a neat theory at least. Thanks for indulging my banter.

    • I like the commentary, thanks. I’m not sure if we have actually learned our lessons from the history of land use in these regions. Sometimes I think that we’re reading along and learning as we go, but deforestation leads to mining abuse to act-now fracking and think about it later activity, to… Money seems to talk louder than the long-range sensibilities, at least to me. In New York I’m glad we’re dragging our feet before the fracking legislation hits the books and permits are granted.


  6. Dale Houseknecht says:

    I have noticed at my cabin in potter co when the beaver are active on our spring run the brook trout numbers are up, and when they move over the ridge into another run the brooky numbers fall off. the beaver move back and forth ,when there food source gets depeated on the run, when the willows grow back in a year or two they come back and so do the brookies.

    • Dale, This seems to suggest that when the dams are fresh the brooks have some temporary holding water, and when the pools begin to fill in, the beaver and trout move on. A sustainable pattern if the streams stay cool enough. Thanks


  7. The notion that beaver ponds have warmer water temperatures is simply not true when you look at the issue of pond depth and the cooling effect of hyporheic exchange. Check out this slide from NOAA fisheries Michael Pollock.

  8. Heidi,
    I’ll respectfully disagree with you on this point. A careful reading of the post will indicate that I, too, admire the wild beaver, but the subject here is not how beaver dams are good for the environment (yes, beaver ponds attract a variety of birds and other animals that are “beneficial”) but how they impact small native trout streams in the East where habitat conditions are already somewhat compromised. Please show me data suggesting that beaver ponds in the eastern U.S. are beneficial for native trout that require water temperatures less than about 65 degrees F. in order to survive.

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