Bültsee (Danish: Bulsø) is a lake in Rendsburg-Eckernförde, Schleswig-Holstein, Germany.

At an elevation of 9.35 m (30.68 ft), its surface area is 0.078 square miles (20.10 ha).

The name derives from Old Danish bolt in the meaning round increase (cf.

*bhel≈to swell, to bubble, to be round).

This Schleswig-Holstein location article is a stub.