The European Commission is taking France to the EU Court of Justice for not doing enough to fight against green algae water pollution.
Environment Commissioner Janez Potočnik revealed the move saying France had failed since 1991 to take measures to guarantee that water pollution by nitrates is addressed effectively.
Green algae has invaded beaches in Brittany and Normandy; linked to pollution from pig-farming in one and stable wastes in the other.
When the algae rots it gives off noxious gas hydrogen sulphide – which led to the death of a horse being ridden on the beach in Saint-Michel-en-Grève in 2009. The horse owner fell unconscious after breathing fumes.
Last summer nearly three dozen wild boar were found dead on Brittany beaches.
Commissioner Potočnik said: "Even though the Nitrates Directive has been in force since 1991 ... it remains for France to adopt measures to effectively fight against this pollution."
French officials have been told to identify the areas most affected by pollution and implement action plans to combat the pollutant.
The Ecology Ministry denied nothing has been done, saying: "We have initiated reform. But we must wait until mid-2013 before it will be effective."
The move comes just days after Ecology Minister-Morizet quit the government to become Nicolas Sarkozy's official spokesperson.