The Plan du Lac is a grassland lake. The banks are alive with rushes and sedges. The bottom is lined with stoneworts, edged by some broad-leaved pondweed. The lake is stocked with brown trout and schools of minnows wander here and there. It’s a good breeding ground for the common frog. The permeability of the limestone substratum leads to a significant drop in the water level at the end of the season.