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One of the main issues is that dams tend to block access to the upstream spawning grounds for species such as Coho salmon. E.g. see https://www.reuters.com/worl

• bilekas 3y ago
  Not sure how prevalent they are bit aren't fish ladders built with dams for this exact reason? https://www.sciencedirect.com/science/article/pii/S0925857416305936 https://www.sciencedirect.com/science/article/pii/S092585741...
  • burkaman 3y ago
    Yes, but it's very hard to get fish to use them. Some species are almost completely blocked even if there is a ladder.
  • bobthepanda 3y ago
    They don't work for many species. For example, one study found that 3% of American shad were able to use a fish ladder. https://e360.yale.edu/features/blocked_migration_fish_ladders_on_us_dams_are_not_effective https://e360.yale.edu/features/blocked_migration_fish_ladder... Fish ladders are akin to greenwashing.
  • belorn 3y ago
    Fish ladders are expensive and have a fairly large negative impact on yearly electric output. Forcing upgrades makes most dams too expensive, which would mean they get replaced by fossil fueled power plants which can more cheaply operate as backup for wind and solar. As a result, most hydro power in Europe is in direct violation of environmental laws, but are also given exceptions given the yearly and regular energy crisis.