Neighbour's fosse floods our land

Our recently bought property is bordered on one side by a drainage ditch, owned by the neighbouring vintner. A second neighbour empties her fosse and wine processing waters into this ditch. Neighbour 1 has not made use of this drainage and has now filled in the ditch (elevating his land approx. 2 meters and probably also spilling his landfill onto part of our land). This is now resulting in the waste waters of neighbour 2 flooding straight onto our land, close to our pool! How can I resolve solve this?!

Whatever else people suggest, first of all:
Speak to the Marie
Write to both your neighbours (avis recommandé) explaining what is happening and saying you need the ditch “fauchaged”


Marie is always your best first port of call.

Mairie and then seriously consider notaire (unless @spj says not to bother).

Reason being that it seems when you send official notices often you have to make referral to xyz
“Decret” or other law by its correct name, for it to be valid.

This sort of stuff about land rights is meat and drink to notaires and they should know it off the top of their head and what it takes to enforce action.