Eau Noire River in Nismes

The Eau Noire is a source river of the Viroin that rises at Cul-des-Sarts in the extreme south of the province of Namur at an altitude of 350 meters. Shortly after the source, it forms the border with France for about five kilometers before turning northwards. Just past Couvin, the main riverside town, part of the river goes underground through the Grottes de Neptune also known as "Grottes de l'Adugeoir". The underground branch merges again with the main stream at Nismes. At the "Roche à Lomme" the Eau Noire merges at 150 meters with the Eau Blanche to form the Viroin. (Wikipedia)

The river was a bit interspersed with algae, which is very nice to look at.

nice place with carved rocks.
pay attention when wet.