This lake is an important stopover for the cranes (grus grus) on their way to their wintering quarters mainly in Spain. It was opened in 1974 and is meant to regulate the waters of the Marne river and protecting in this way Paris from inundations. It is one of the biggest in Europe (4800hectares) and cycling around it will put some 35km on your meter.
In the late seventies it was becoming clear for us that the cranes had started using it as a fueling station on their migration route and from then on we started visiting the place ones or twice a year and we saw numbers grow every year. The birds sleep on the islands in the lake where they are safe from non avian predators. With this link https://champagne-ardenne.lpo.fr/grue-cendree/grus/lac-du-der you can have a look at the fluctuating numbers since LPO has started counting them.
On November the 3rd a new record number of about 268,000 birds were counted. This however does not mean that the species is thriving (breeding was not good this year). It was only due to the weather conditions. These birds are so much better than all the weathermen together! There were birds arriving every day but nobody left. On our visit last week we noticed that there were only few juveniles among them (juveniles have more brown on neck and head and they have a different call).
In the morning around sunrise they leave for the fields around the lake to feed and in the evening around sunset they return to sleep. Depending on the weather conditions this can be an unforgettable spectacle. Nowadays hundreds of people come to watch it (in the seventies and eighties we only saw hunters but now people with binoculars and camera's are everywhere). This sparsely inhabited region has surely benefited from this event. Accommodation, restaurants, campervan sites and even a casino and tourist office it is all there now; and even a photo festival is organized every year in November for the 24th time already this year.
More pictures in the 'Lac du Der' photo album on my website https://www.julienherremansphotography.com