Critical habitats for cold-water species are anticipated to diminish as global climate change reduces summertime availability of cold water in streams.  Warming of summer flows is expected to reduce populations of culturally and economically important cold water species such as trout and salmon.  An exception to this trend is spring-fed streams in volcanic terrains throughout the Pacific Ring of Fire (e.g. Cascades, Andes, New Zealand, and Kamchatka).  These streams are fed by extensive, long residence time aquifers that produce reliably cool summer baseflow.  The Fall River, one of the best kept secrets in Northern California, is one of the streams that provides reliable cool water during the warm summer months, even during the extreme 2012-2016 and 2020-2022 droughts in California.  The UC Davis Center for Watershed Sciences (CWS) has been studying the rainbow trout population of the Fall River since 2013 to better understand how the Fall River functions as a cold water refuge for this important fishery.