The Marne reservoir-lake or Lac du Der-Chantecoq was operational from 1974. The purpose of this artificial lake is to reinforce the flow of the Marne during low-water periods and to reduce the risk of flooding downstream. The low-water support, which normally takes place from the beginning of July to the end of October, can provide an average of 30 m³/s additional flow to the Marne. The structure functions as a weighting instrument: the level of the water plan fluctuates according to the needs of the Marne and the Blaise, the two rivers regulated by the lake.