The Cuivre River originates in northeast Missouri, in Audrain and Pike counties. It flows southeast through Pike, Montgomery, Lincoln, Warren and St. Charles counties to its confluence with the Mississippi River at river mile 236.5 (measured from the mouth of the Ohio River) near Winfield, Missouri (Figure Lo01). The watershed drains 1,235 square miles of the Upper Mississippi River Basin. Its two major tributaries are the West Fork Cuivre River and the North Fork Cuivre River. Other major streams include Big Creek, a tributary to the Cuivre River; Elkhorn Creek, a tributary to the West Fork Cuivre River; and Indian and Sulphur creeks, both tributaries to the North Fork Cuivre River.