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.