The water in the river Dordogne got warmer during this hot summer. For a number of aquatic plants this created the right circumstances for an explosion of new vegetation. Here, just above a dam, the river is calm and two different kinds of Waterweed weave their snake-like shoots.
The big snakes are shoots from Brazilian Waterweed (Egeria densa) and the small snakes are from Curly Waterweed (Lagarosiphon major). Both come from hotter parts of the world, The first one from Latin America, and the other from Southern Africa. May be they escaped from an aquarium or came along with a ship. Anyhow, now they are here and thriving. Or should you say, invading?
And yes, it is in full bloom. The flowers float on the water surface on long thin stems. In France, Brazilian Waterweed only makes male flowers and breeds by loosing its shoots. They float with the river or are taken by ducks and swans.