Recent study finds larger fish populations in colder waters
Low river flows and associated high water temperatures often negatively affect fish populations. Biologists believe this to be the case in the Deschutes River downstream from Bend, where flows are dramatically altered during the irrigation season. Conversely, increased river flows, lower water temperatures and cold spring inputs often benefit native fish and lead to more abundant populations. With limited access to this reach of the Deschutes River, there has historically been little data to show how fish populations here respond to increased summer flows or to what extent fish congregate in cold water areas.
Recently, Oregon Department of Fish and Wildlife, in partnership with the Upper Deschutes Watershed Council, completed the first year of a study of fish populations and habitat use in the Deschutes River between North Canal Dam near the Riverhouse Hotel in Bend and Steelhead Falls located near Culver. The preliminary findings of this five-year study confirm that higher flows and areas of cooler water support higher numbers of redband and brown trout. It also suggested that fish are bigger at cold-water sites and that current flow management in the Deschutes River may benefit introduced brown trout at the expense of native redband populations.
Since 1999, the Deschutes River Conservancy has been working with water users to restore flows to this section of the Deschutes. Before restoration efforts began, flows in this part of the river would drop dramatically during the summer irrigation months to as low as 30 cubic feet per second (cfs). Today, thanks to the participation of local irrigation districts, up to 160 cfs of water is now protected instream during these hot summer months.
This study will allow conservation groups such as the Deschutes River Conservancy and the Upper Deschutes Watershed Council to have the scientific data needed to identify conservation and restoration priorities, develop and implement large scale restoration projects, and further improve conditions for fish and other wildlife.
This study was supported in part by the Central Oregon Irrigation District Mitigation and Enhancement Fund.