Simssee is a lake in the Alpine foothills of Bavaria, Germany.

Its has an elevation of 470.1 metres and a surface area of 6.5 km2, making it the largest lake in the Rosenheim district.

The retention period of the Simssee is about one and a half years and its catchment area covers 59.51 km2.

It is the last remain of Lake Rosenheim, which stretched over the area at the end of the Würm glaciation.

The lake is a popular recreational spot for local visitors.