With a surface area of 4,800 hectares, the Lac du Der-Chantecoq is the largest artificial lake in mainland France. Designed to protect Paris from flooding, the lake regulates the flow of the Marne river, an affluent of the Seine. Its average depth is shallow – four to seven metres – with a maximum of eighteen metres. It owes its name both to the Der country, the natural region where it is located, and to the village of Chantecoq, which was destroyed along with those of Champaubert-aux-Bois and Nuisement-aux-Bois during the construction of the lake. Its capacity is 350 million cubic metres of water.