Courtille

France Lake 2 - Good

Courtille is a recreational lake located south of Guéret in France, originally formed as a succession of mill ponds and formally developed as a leisure amenity in 1985. The lake serves as a major tourist and recreational hub offering swimming, fishing, sailing, walking trails, dining, and sports activities. The water body has experienced significant cyanobacteria blooms over the past decade, necessitating regular monitoring and management actions. Water quality monitoring over eight years (2017–2024) has shown excellent quality from 2017 to 2022 and good quality in 2023 and 2024.

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Water

Artificial lake (plan d'eau aménagé) with a surface area of 220,000 m². The watershed has a surface area of 5.3 km² with elevation ranging from 683 metres at the highest point (Maupuy) to 453 metres at the outlet. The lake is fed by three streams: Ruisseau de la Naute, Ru de Fayolle, and a third stream to the southwest. The substrate is predominantly mud (vase) with artificial sandy beaches in some zones.

Location

South of Guéret (23000), France. The lake is a major attraction for Guéret and surrounding municipalities.

Season

Official monitoring occurs annually with intensified monitoring during the bathing season. The bathing season appears to be summer months (July–August), though closures have occurred during this period in past years due to cyanobacteria.

Water Quality

Classification as Type 1 bathing profile based on excellent water quality from 2017–2022 and good quality in 2023–2024 according to the Directive 2006/7/CE. Sediment phosphorus concentration at the water-sediment interface averaged 766.5 mg per kilogramme of dry matter in March 2023, significantly above the 600 mg threshold, indicating sufficient phosphorus to sustain cyanobacteria proliferation. Phosphorus levels are homogeneous across the entire lake with no variation exceeding ±20% from the average.

Risks

Cyanobacteria blooms are the primary identified risk, particularly during summer months (July–August). Swimming was completely or nearly prohibited during July–August in 2015 and 2016 despite recent dredging in autumn 2014. The high sediment phosphorus concentration supports sustained cyanobacteria development. Historical monitoring since the mid-1990s has documented periodic closures due to cyanobacteria proliferation.