We saw way too many of these signs. Loosely translated, that "inondée" indicates an inundated (aka flooded) road.
We walked through one inundation, above, and rode through another that had our feet fully under water as we pedaled, maybe 12" deep.
Then there was the tree.
But let's start at the proper beginning of the story..
Our campgrounds at Melun were idyllic -- outdoor chess set, playground, and right on the Seine River.