Siltcoos Lake (silt’-koos), at 3,164 acres (1,280 ha), is the largest lake on the Oregon Coast of the United States. Fed by runoff from a basin of about 68 square miles (180 km²) in Douglas and Lane counties, it is located about 7 miles (11 km) south of Florence and 0.5 miles (1 km) east of U.S.