At the heart of the department, the Marne (24 km) forms the famous Boucles de la Marne, place of recreation at the edge of the water from the nineteenth century.
The Marne has a meandering course typical of lowland rivers. It crosses the Val-de-Marne from Bry-sur-Marne and Perreux-sur-Marne (upstream) to Alfortville and Charenton-le-Pont (downstream) where the Marne flows into the Seine at confluence site, overlooked by the Chinagora Hotel.
The Marne has 25 islands, 3 of which are classified as a Departmental Nature Reserve. It includes the islands of the Drinking water in its downstream part and the two small islands of the Gords and Pissevinaigre. They can be seen from the Pont de Champigny and then along the banks of the Marne, in the Boucles de Saint-Maur. The islands of Gords and Pissevinaigre are completely natural and are characterized by a dense floristic richness and especially by the presence of rare plants. They are forbidden to the public, but it is possible to discover them by canoe, kayak, electric boat or during a cruise.