Plan D'eau Communal

France Lake 0 - Not classified

The Pertre municipal lake is a recreational freshwater body created in 1989, located in the heart of the commune of Pertre in Ille-et-Vilaine. It serves as the source of the Seiche river and is used for swimming during the summer season and fishing year-round. The lake has a maximum length of 145 metres, maximum width of 104 metres, and covers approximately 1.3 hectares. It is fed by underground springs and rainfall runoff, and includes a walking path around its perimeter.

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Water

Freshwater lake with maximum length 145 metres, maximum width 104 metres, surface area approximately 1.3 hectares. Fed by underground springs and rainfall runoff. Contains a downstream secondary lake connected via overflow. A bottom valve allows the lake to be drained for maintenance.

Location

The Pertre municipal lake is located at the centre of the commune of Pertre, at the boundary between Mayenne and Ille-et-Vilaine departments. The commune has 1,385 inhabitants. The bathing beach is on the northern shore of the lake.

Facilities

Bathing beach with sandy surface approximately 325 square metres. Information panels at the main entrance. Sanitary block. Children's play area. Sports facilities including football and beach volleyball areas. Walking path around the lake. Dog waste bag stations. Wooden barrier separating beach from pedestrian path.

Season

Bathing is authorised during the summer season. A 16-week monitoring period is common to all Breton bathing sites, from 2004 to 2014 onwards.

Water Quality

Cyanobacteria monitoring has been continuous since 2004. Between 2004 and 2019, WHO alert level 3 (exceeding 100,000 cells/ml) was exceeded systematically during all or part of the bathing season in most years except 2007, 2008, and 2013. In 2004, 2005, 2011, and 2012, level 3 thresholds were exceeded throughout the entire monitoring season. Five groups of cyanobacteria species have been identified, with three groups containing potentially toxic species representing on average 31% of cyanobacteria populations over 11 years. Aphanizomenon species constituted 45% of cyanobacteria populations and 66% of potentially toxic species populations.

Risks

Cyanobacteria proliferation is a confirmed and regularly observed risk, classified as Type 2 profile risk. Multiple potentially toxic cyanobacteria species are present, including Aphanizomenon species which are known producers of multiple families of toxins.