Water-temperature, air-temperature, specific-conductance, wind-speed, and solar-radiation data are presented from a study conducted in the Tualatin River Basin in northwestern Oregon during 7-month periods from May 1 through November 30, 1994 and May 1 through November 30, 1995. The study was done to assist local and State agencies in understanding temporal and spatial patterns of water temperatures in the river, determining the relation between water temperature and human activities, and developing urban and agricultural management strategies for controlling impacts on stream temperatures. Data were collected at 14 fixed-station continuous monitoring sites located on or near the main stem and major tributaries. Data from temperature and specific-conductance sites were collected instantaneously every 30 minutes on the hour and half hour. Wind-speed and solar-radiation data at two sites were averaged every 60 minutes. Wind-speed and solar-radiation data at a third site were averaged every 30 minutes. Water temperature data were also collected during seven synoptic surveys near the two main wastewatertreatment plants. The surveys were conducted during the low-flow period from August to October of 1994 and August to September 1995. During each survey, up to six recording temperature probes were positioned at locations upstream and downstream of plant effluent outlets. The probes collected data every 16 minutes over 48-hour periods.