The Steinhuder Meer or Lake Steinhude is a lake in Lower Saxony, Germany located 30km northwest of Hanover. It is named after the nearby village of Steinhude. It has an area of about 30km², making it the largest lake of northwestern Germany, but it is very shallow, with an average depth of only 1.35m and a maximum depth of less than 3m. It lies within a region known as the Hanoverian Moor Geest.GeologyIt is part of the glacial landscape formed after the recession of the glaciers of the latest Ice Age, the Weichselian glaciation. There are two theories regarding how the lake of Steinhude was formed. One of them says that glaciers gouged out the hole and meltwater filled it. The other theory states that an ice storm formed the hole and as the groundwater rose, the lake was created. In its middle there is a small artificial island carrying an 18th-century fortification, the Wilhelmstein. Today the lake is the heart of a nature reserve, the Steinhuder Meer Nature Park, and is also used as a recreational area.IslandsThe lake has two islands, both of them artificial:  Wilhelmstein (12,500 m²) off Hagenburg was built between 1761 and 1765. It was turned into a military fortress between 1765 and 1767 by William, Count of Schaumburg-Lippe. Afterwards it briefly served as military school (one of its graduates was Gerhard von Scharnhorst who later became Chief of the Prussian General Staff). From 1777 until 1867 the island was used as state prison of the Principality of Schaumburg-Lippe. Badeinsel Steinhude (35,000 m²) was built in 1975 using sand retrieved from the lake. It has a sandy beach which is popular during summer; a service center is available. Access to the island is via a 80m pedestrian bridge from Steinhude.