Clark Lake is situated in Clark County, approximately 8 miles east of Springfield, northeast of Harmony, off US-40. Clark Lake is a headwater impoundment of Sinking Creek in the Great Miami River watershed. The Clark Lake watershed comprises approximately 4,384 acres, of which 80 percent is agricultural land and 8 percent woodlots. Construction of the earthen fill dam on Sinking Creek began in 1956 and was completed in January 1958.