The city of Tulsa, Oklahoma, uses Lake Eucha and Spavinaw Lake in the Eucha-Spavinaw Basin in northwestern Arkansas and northeastern Oklahoma for public water supply (fig. 1). Construction of Spavinaw Dam (U.S. Geological Survey lake-level station at Spavinaw Lake, station identifier 07191300, fig. 1) on Spavinaw Creek began in 1922 and was completed in 1924 (Oklahoma Water Resources Board, 2002). A series of pipelines 60-miles long was constructed to transfer water from the base of Spavinaw Lake Dam to a wastewatertreatment plant in Tulsa.