Otsego Lake is a small lake located in Otsego County, New York in the USA and is the source of the Susquehanna River. Cooperstown, New York is at the southern end. Glimmerglass State Park is located on the northeastern shore. Glimmerglass Opera is located on the western shore. Otsego Lake is nine miles (14.5 km) long. It is geologically related to the Finger Lakes, but is not counted among them.