Fly Fishing’s Future - Are Dams Good or Bad for Trout?

It’s complicated. But, generally speaking, pretty damn bad.

Stagecoach Dam, in northwestern Colorado. | Photo by Jasper Taback

For better or worse, there are more than 80,000 dams on rivers in the United States. Some serve essential purposes—irrigation, flood control, hydropower generation — but many are no longer in use, sitting and deteriorating in the rivers they impound.

Unfortunately, dams significantly impact our trout populations and the rivers they call home. Should all dams be removed? Probably not. Should most of them be removed? Absolutely.

Blocked Migration

The most glaring problem a dam poses for trout is movement up and down the river. Trout don’t migrate the same way that steelhead or salmon do, but they move throughout their home river, occupying different stretches at different times of year. 

Trout need to move for several reasons: to feed, spawn, and find shelter. When a river is dammed, it doesn’t allow trout to do what they need to survive and reproduce. 

Changes in Water Temperature 

Some dams regularly release cold water from deep in the reservoir, creating suitable conditions for the trout living below them. In fact, the United States has shown that it can create excellent conditions for trout. But not all dams release cold water. 

Dams that don’t release water or that release water irregularly create stagnant water downstream. Because the water is moving more slowly, it gets more exposure to sunlight, causing the water that flows downstream to warm. Trout need cold, oxygen-rich water to survive, not warm water. 

Changes in Water Flow

Slower flows do more than affect water temperature – they mess with a trout’s ability to feed and spawn. Trout rely on fast-moving water to bring them food and keep the eggs they lay in gravel beds oxygenated and clean. Without the river’s typical fast flows, insect populations dwindle and sediment builds up, preventing oxygen flow to eggs. 

Keeping Trout Habitats Natural

Trout have adapted to survive and thrive in cold rivers – when those rivers get dammed, conditions are introduced that trout aren’t equipped to handle. Dam removal efforts have grown tremendously in recent years, but tens of thousands still affect trout populations across the country. Trout rivers are meant to be wild places – it’s important to keep ‘em wild.