Aasee, Artificial reservoir in Münster, Germany

Aasee is an artificial reservoir southwest of Münster's centre, about 2.3 km long, up to two metres deep and covering 40.2 hectares. It dams the Münstersche Aa and is ringed by lawns and trees, with roughly 10 km of paths and about 18 hectares of meadow. A long planked wooden dock with a T-shaped shore section and a lantern-topped pole juts over the water.

Work started in 1914 but was halted by the First World War and only finished two decades later. The basin was created mainly to prevent flooding from the river Aa in the city center.

The name Aasee comes from the small river Aa that was dammed to form this body of water. Students and families gather on the grassy banks to read, picnic or simply lie in the sun on warm afternoons.

A hiking and jogging trail of about 5.7 km leads around the lake, so a full circuit takes roughly an hour at walking pace. The water level can fluctuate by up to a metre, and the banks include shallow water zones. Boat rental, a boating school and three sailing clubs operate on the water; the Aaseeterrassen at the northern, city-side end were opened in 2008.

The lake hosts Germany's oldest hot-air balloon gathering, the Montgolfiade, held on the Aasee meadows since 1969 and organised each August by the Freiballonsport-Verein Münster und Münsterland with the city's sports department. The same water has hosted the German Rowing League since 2009, and in October 2013 the 100th German championship for eight-oared boats over the long distance took place here.