Well, still no word from the Department of the Interior on cool mix flows from Glen Canyon Dam. The last two years, about this time, releases around the dam through the bypass trunnels have kept water temperatures in the upper 50’s through the hottest part of the summer. These flows were to prevent the spawning of smallmouth bass down in Grand Canyon, where they are considered a threat to the native fish. Our trout in the Lees Ferry stretch have been an incidental beneficiary of these flows. In 2022 the temperatures went to 70 degrees in the Lees Ferry stretch and we lost about half our fish in the winter of 2022-2023 because of that warm water.
The warmer flows effect trout in two ways. First, warmer water gives up it’s dissolved oxygen more easily so dissolved oxygen levels fall. Anything below 4 milligrams per liter is the in the red zone for trout. Secondly, warmer water increases the metabolism of fish. They need to eat more to survive, but the warmer water doesn’t mean there is any more food. Condition of the fish is diminished and they have a harder time surviving the winter months when food availability is low. That is what happened in 2022.
Let’s hope the DOI acknowledges the value of this fishery and implements these flows!