Beaver Dam Activity Impacts on Fish

A review by Kemp et al (2012) revealed that many of the percieved impacts of beaver dams on fish are based on conjecture and heresay. This is not to suggest that there are never negative impacts on fish, just that perceptions amongst fish biolgists and managers have strong bias.

Kemp PS, Worthington TA, Langford TEL, Tree ARJ and Gaywood MJ. 2012. Qualitative and quantitative effects of reintroduced beavers on stream fish. Fish and Fisheries. 13(2): 158-181. DOI: 10.1111/j.1467-2979.2011.00421.x.

Fish Passage

Beaver dams can act as a barrier (typically temporarily or seasonally) to upstream and downstream movement of fish. Too often, this is assumed to always be detrimental. However, for many native fish that co-evolved with beaver dam activity in the systems, beaver dams are passable and not a problem. Moreover, the fact that beaver dams tend to lead to the creation of both more, and more diverse aquatic habitat tends to offset negative impacts for many native fish. For many fish who pass upstream of beaver dams with ease, this tends to correspond with when they spawn and that migration tied to higher flows.

Studies on Fish Passage over Natural Beaver Dams

Lokteff RL, Roper B and Wheaton JM. 2013. Do beaver dams impede the movement of trout? Transactions of American Fisheries Society. DOI: 10.1080/00028487.2013.797497.
Cutting KA, Ferguson JM, Anderson ML, Cook K, Davis SC, Levine R. 2018. Linking beaver dam affected flow dynamics to upstream passage of Arctic grayling. Ecology and Evolution 8 : 12905–12917. DOI: 10.1002/ece3.4728
Malison RL, Eby LA, Stanford JA. 2015. Juvenile salmonid growth, survival, and production in a large river floodplain modified by beavers (Castor canadensis). Canadian Journal of Fisheries and Aquatic Sciences 72 : 1639–1651. DOI: 10.1139/cjfas-2015-0147
Malison RL, Kuzishchin KV, Stanford JA. 2016. Do beaver dams reduce habitat connectivity and salmon productivity in expansive river floodplains? PeerJ 4 : e2403. DOI: 10.7717/peerj.2403

Studies on Fish Passage at BDAs

Bouwes N, Weber N, Jordan CE, Saunders WC, Tattam IA, Volk C, Wheaton JM and Pollock MM. 2016. Ecosystem experiment reveals benefits of natural and simulated beaver dams to a threatened population of steelhead (Oncorhynchus mykiss). Scientific Reports. 6: 28581. DOI: 10.1038/srep28581.
Pollock MM, Witmore S, Yokel E. 2019. A field experiment to assess passage of juvenile salmonids across beaver dams during low flow conditions in a tributary to the Klamath River, California, USA. bioRxiv : 856252. DOI: 10.1101/856252

What does fish passage look like?

Fish often use the mattresses in front of a dam to make their way up and over a dam:

Fish do not always make it successfully over a dam, but under different flow conditions that story may differ. Here, a minor breach in a dam presents some challenges for this fish:

In fact, beaver dams could even help control non-native species. In Utah’s Logan River, Lokteff et al. (2013) found that native cutthroat trout navigated beaver dams more successfully than introduced brown trout. So that’s neat. #WorldFishMigrationDay pic.twitter.com/elvQDMADvD
— Ben Goldfarb (@ben_a_goldfarb) April 23, 2018

If you’ve ever seen this sticker, the video below will give some creedence to that. Jumping is probably not the most common way most fish make it over beaver dams (using a mattress or overflow channels is likely more common). Neat footage all the same:

Many misinterpret any struggle or failed passage over beaver dams as necessarily a bad thing. However, disregarding that interpretation, the video below shows some interesting footage.

Other Fish Passage Resources

Fish Passage - Who Cares? - Presentation by Greg Apke (ODFW)
Fish Passage Devices at Beaver Dams - Beaver Solutions
ICER Studies on Impact of Beaver (CAstor fiber) on fish
Wild Trout Trust View on Beaver-Trout Interactions
Beavers and Fish Fact Sheet - From [Miistakis Institute](https://www.rockies.ca and Cows and Fish Leave it to Beavers Watershed Stewardship Program

Can’t believe I missed #WorldFishMigrationDay, one of my favorite holidays. Appropriately, I was out fishing.

To belatedly celebrate, here’s a quick thread about migratory fish and — of course — #beavers. pic.twitter.com/aZSjuJXebq
— Ben Goldfarb (@ben_a_goldfarb) April 23, 2018

State Policies with Regards to Fish Passage

Special Case of Oregon Department of Fish and Wildlife

Oregon has a fish passage law (ORS 509.585), which initially caused some concern for how low-tech PBR projectswere permitted in fish-bearing streams. In 2020, ODFW progressively updated their fish passage policy to explicitly address and allow a pathway for LTPBR structures to proceed if they meet certain guidelines (including following the design principles in the LTPBR manual).