For many years, federal, state, and corporate proponents of building more dams in California have touted cold water river releases provided by increased water storage behind dams as a key tool in saving struggling salmon and steelhead populations.

Yet a just published study by the UC Davis Center for Watershed Sciences has found that dams are ineffective for the cold water conservation that is needed to preserve imperiled salmon, steelhead, and trout.

Dams poorly mimic the temperature patterns California streams require to support the state’s native salmon and trout, more than three-quarters of which risk extinction, according to the study published in the journal PLOS ONE by the University of California, Davis. Bold actions are needed to reverse extinction trends and protect cold-water streams that are resilient to climate warming.

The study helps identify where high-quality, cold-water habitat remains to help managers prioritize conservation efforts.

It is no longer a good investment to put all our cold-water conservation eggs in a dam-regulated basket, said lead author Ann Willis, a senior staff researcher at the UC Davis Center for Watershed Sciences and a fellow for the John Muir Institute of the Environment. We need to consider places where the natural processes can occur again.

Understanding where cold water is likely to stay cold is critical for conservation, according to the study. But cold is more than just a number on a thermometer. The term represents the many factors that combine to create cold water capable of supporting aquatic ecosystems.

Water managers deliver cold water from reservoirs to streams to support aquatic life, but Willis said this assumes that all cold water is the same, akin to giving blood to another person without understanding their blood type and health status.

While previous studies have suggested that dams can be operated to achieve ideal temperatures, few tested that hypothesis against the temperature patterns aquatic ecosystems need, the study reveals.

The UC Davis study assessed stream temperature data from 77 sites in California to model and classify their thermal regimes, or annual temperature patterns. It found the state’s reservoirs do not adequately replicate natural thermal patterns, making them incapable of supporting cold-water species effectively.