Arendsee, Sinkhole lake in northern Saxony-Anhalt, Germany

Arendsee is a large natural lake formed by the collapse of a subsurface salt dome in Saxony-Anhalt, featuring steep banks and significant depth. The water body is surrounded by forested shores, creating a contained basin distinct from other regional water features.

Arendsee lies over a salt dome whose leaching caused the ground above to collapse repeatedly. Documented collapses occurred in 822 and again in 1685, when the local mill sank and the lake is said to have grown by 20 hectares at once. The name Arnseo appears in Frankish annals for the 822 event, so the lake already had a recorded name then.

The name Arendsee was recorded as Arnseo in the annals of the Frankish Empire in connection with the 822 collapse, though a legend instead credits a miller named Arend whose mill sank in 1685; the name likely derives from "Aar", the sea eagle. A roughly ten-kilometre walking and cycling path circles the lake, passing weekend cottages and woodland of black alder, oak and pine.

During warmer months, designated swimming areas and boat launches are available around the lake shore at several access points. Be aware that steep banks make water access challenging in many locations.

Water renewal in this lake happens extremely slowly because it remains largely isolated from other water systems with minimal exchange. This isolation creates a closed ecological system that functions quite differently from neighboring lakes.