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.
On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream most seriously weakens the argument.