CHARACTERISTICS AND FREQUENCY OF COOL-WATER AREAS IN A WESTERN WASHINGTON STREAM

Four distinct types of cool-water areas were located during this mid-summer survey of Thrash Creek, Washington, a warm, 5th-order stream. These areas were termed lateral seeps, pool bottom seeps, cold tributary mouths and flow through the bed, depending on the entry point and source of the cool water. These types differed with respect to average size, depth and location in the stream channel. Temperatures in the cool water areas averaged 4.7.degree. C lower than ambient streamwater on warm afternoons. Such spots (39) were located on a 3.5 km reach of the study stream. They accounted for 1.6% of the surface area and 2.9% of the water volume on this stretch of stream.