To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam  Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season  But in the first season after the project's completion, only 300 per day made the journey
Clearly, the fish pass is defective
The construction of the dam stirred up potentially toxic river sediments that were carried downstream.