The trouble(s) with water and the Endangered Species Act. Here’s an excerpt:
One of the most important ”river law” topics is the application of the Endangered Species Act to water management and use. The ESA is a crucial law for western rivers because it has been far more influential than anything else in making the environment a relevant factor in water management, especially in the operation of federal water projects. And federal river restoration efforts are overwhelmingly driven by ESA considerations.
More endangered/threatened species coverage here.