Cold Water Refuges: Rethinking 'Fishable' for Large Pacific Northwest Rivers

摘要

CLEAN WATER ACT water temperature protections have traditionally looked at the daily maximum temperature midstream. But in grappling with protection of salmon in the Pacific Northwest, a new focus of protection and enhancement is emerging for large rivers-cold water refuges. This will become particularly important in future years as rivers warm up from predicted climate change impacts. Yet integrating cold water refuges into the structure of Clean Water Act regulations, such as water quality standards and total maximum daily Loads (TMDLs), is proving very challenging. The path forward remains far from clear. The Pend Oreille River pours out of Lake Pend Oreille in Idaho and then flows through Washington into the Columbia River in Canada. The issue of cold water refuges (CWRs) first emerged for me as I developed a temperature TMDL for the Pend Oreille River. Despite the presence of three dams on the river, our modeling found that the river had always been quite warm, due to surface waters leaving the lake and flowing through a wide, open valley. Radio tag studies showed that bull trout were hiding in the mouths of cool tributaries and holding up near springs. The fish that stayed in the river died. However, because our water quality standards (WQS) regulate the temperature in the middle of the river, we have always focused on the question of what drives midstream temperatures. Now I was wondering: were we asking the wrong question?