| > You get many of the same environmental benefits (lake area no longer flooded, fish can traverse the base of the dam) Besides the fact that the lake area will still be partially flooded, as other replies have said, fish are complicated and there are a lot of dam related issues that affect fish passage. Just a few: - Downstream passage would have to be through spillways. Survival rates are pretty good (95%+) [1], much better than turbine passage, but not as good as not having a dam in the way. - Conventional spillways open from bottom, which fish have a hard time finding. [2] Granted, if the water levels are reduced this could be less of an issue. - Time spent in slow moving water increases predation on salmon. [3] If you visit a dam you'll see ospreys all around. Slow water can also favor some species over others. - There are a bunch of other water quality issues that dams cause, most notably water temperature. The 2002 Klamath fish kill [4] (the largest in history and a major impetus for un-damming the Klamath) was caused by high water temperatures. [5] - Even shadows can cause significant issues, from structures as small as docks or piers. [6] - Upstream passage is not solved by opening the spillway and would still be an issue, requiring fish ladders or transportation. All the existing problems with fish ladders apply. [7] - Besides salmon and trout, other important species get blocked by dams, including sturgeon and lampreys [8], and each are affected by dams in their own way. [1] https://www.salmonrecovery.gov/Hydro/Structuralimprovements/... [2] https://www.fisheries.noaa.gov/west-coast/endangered-species... [3] https://www.fisheries.noaa.gov/west-coast/endangered-species... [4] https://en.wikipedia.org/wiki/2002_Klamath_River_fish_kill [5] https://www.waterboards.ca.gov/waterrights/water_issues/prog... [6] https://wdfw.medium.com/casting-shadows-on-the-sound-3a9a555... [7] https://medium.com/re-form/whats-the-dam-problem-3b5cd839ae7... [8] https://e360.yale.edu/features/sea-lampreys-pacific-lampreys... |