Brittany implements new strategy to combat green algae pollution

The French state is implementing a new strategy to combat green algae proliferation in Brittany, following a court order from the Rennes Administrative Court. The new measures, set to take effect on September 1, 2026, aim to better target agricultural holdings identified as having a high risk of nitrate leaks.

The strategy includes strengthening measures on 20% of agricultural land to protect the most fragile ecosystems while simultaneously easing certain administrative constraints for farmers. This shift comes as water quality in several sensitive sectors has stagnated despite previous regional action programs.

Green algae, which have washed up on Breton beaches since 1971, release hydrogen sulfide gas as they decay, posing significant health and safety risks. A 2021 report from the Court of Auditors noted that over 90% of this proliferation originates from agricultural sources, specifically intensive livestock farming. The issue has led to beach closures, impacts on oyster farming, and has been linked to suspicious deaths, including a jogger in Côtes-d'Armor in June 2025.