Redband trout also have to compete for this limited habitat with increasing numbers of fish acclimated to warmer water, like smallmouth bass and yellow perch. In a summer like 2021, with low river flows, sanctuaries like these are hard to find in a habitat that is already fragmented by the seven dams on the river, all without fish-passage. When water temperatures exceed these levels, fish look for cooler refuges.

In general, rainbow trout prefer temperatures below 20☌ (68☏) and grow best in temperatures between 13-17☌ (~55-63☏) (Bear et al., 2007). As we discussed, coldwater fish are breathing more rapidly in warm water and this increases their uptake of these dangerous pollutants.Īn increasingly warm Spokane River will limit the habitat for native coldwater fish like the redband trout. We know metals like zinc and lead are in our river from historical mining upstream in the Coeur d’Alene basin. The toxic effects of certain chemicals (e.g., pesticides and heavy metals) on fish also increase with elevated water temperature (Ficke et al., 2007). Protozoan infections like whirling disease or “ Ich” ( Ichthyophthirius multifiliis) can be fatal to trout and easily spread if fish are congregating in cooler pools in the river. Warmer water can also increase numbers of bacteria and parasites, and because fish are already stressed by the heat, their immune systems are not as capable of fighting off diseases (Ficke et al., 2007).

Spokane weather in july