Cyanobacteria Treatment for Lac de la Dathée Sparks Controversy in Vire Normandie

Published February 23, 2026

Vire Normandie is moving forward with a €50,000 plan to combat recurring cyanobacteria blooms in Lac de la Dathée, a site serving as both a drinking water reserve and a developing “nature sports resort.” The proposed solution involves installing “cyanoboxes,” devices that leverage ultrasound to eliminate cyanobacteria. Though, the plan has drawn criticism from local resident Séverine Deutsch, who argues it addresses symptoms rather than the root cause of the pollution.

Concerns Over Upstream Pollution

Deutsch, a resident of Champ-du-Boult, has long campaigned against water pollution affecting her land and the lake. She points to evidence confirming the presence of human fecal bacteria upstream from Lac de la Dathée, suggesting that addressing these sources of pollution is crucial. She stated that installing technical solutions in the lake without treating the discharges upstream is akin to “disguising an infection without treating the wound,” and characterized the plan as a “costly headlong rush.”

According to Deutsch, legal expertise has established proof of pollution by human fecal bacteria upstream of the lake’s watershed. She also noted that seven legal procedures are pending before the administrative court regarding the pollution, and a judicial investigation is underway. She described the situation as “a shame for the territory” and “an insult to law-abiding citizens.”

Council’s Perspective

During the Vire Normandie municipal council meeting on February 16, elected official Régis Picot announced the planned installation of the cyanoboxes. Council members expressed regret that recurring pollution prevents leisure and fishing activities on the lake. They view the project as a step towards realizing the lake’s potential as a “nature sports resort.”

Ongoing Legal Battles

The pollution of Lac de la Dathée has led to annual municipal decrees prohibiting fishing and water activities. The most recent decree, issued last summer, remains in effect. The situation is further complicated by ongoing legal proceedings related to the water quality.