Lake Oscawana is a lake at the heart of Putnam Valley, New York State, United States.

The 386-acre (1.6 km2) lake has a depth that ranges from 25 feet (7.6 m) to 30 feet (9.1 m). The lake is fed by a stream from its north end and it drains through a stream at the middle of its eastern shore. It is nestled in between two hill ranges, which provide spectacular views if you climb one.

The lake also features many houses around its edges and a peculiar rock formation (Goose rocks) in the center of the lake, accessible most safely by kayak or canoe. Lake Oscawana provides summer recreation to many of the local residents who use the lake for boating, swimming, fishing, and just laying on one of the lake's several private beaches.

It features a variety of wildlife including fish, Canada geese, water snakes, turtles, and an occasional stork. In the summer it is cleaned regularly by a floating weed harvester which is a sight in itself. In the winter, the lake freezes over and allows for ice skating and ice fishing. Legend has it there are several cars at the bottom of lake from when the ice was not thick enough.