Velký Rybník

Czechia River 1 - Excellent

Velký rybník is a recreational bathing pond located in the Czech Republic with a surface area of 0.5 km². The beach features sandy shores with a gradual entry into the water and stretches for 450 metres. The pond is operated by the municipality of Hroznětín and receives fewer than 1,000 swimmers per day. The site has been subject to multiple bathing bans since 2015, primarily due to cyanobacteria blooms and algal growth.

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Water

Pond with a surface area of 0.5 km² and a basic hydrological characteristic of 21 litres per second. The catchment area (area of influence) is 14.864 km².

Location

Velký rybník is located near Hroznětín in the Karlovarský region of the Czech Republic. The site is situated at an elevation of 468 metres above sea level.

Facilities

Restaurant, toilets.

Season

Official monitoring conducted annually. Bathing bans were issued: 2015 (full year), 2017 (full season), 12 July 2018 to end of season, 18 July 2019 to end of season, 26 June 2020 to end of season, 29 July 2021 to end of season, 14 July to 20 September 2022, 13 July to 10 September 2023, 25 July to 4 October 2024, 7 August to 1 September 2025.

Water Quality

Intestinal enterococci show excellent quality with an increasing trend since 2010. Escherichia coli show excellent quality with a declining trend since 2012. Algal blooms are massive with an increasing trend since 2010. Transparency does not meet the 1-metre limit with a worsening trend since 2010. Chlorophyll a exceeds the limit of grade III with an increasing trend since 2010. Cyanobacteria exceed the limit of grade III with an increasing trend since 2010. Overall monitoring assessment: satisfactory condition. Natural pollution is locally significant, including pollen, plant debris, leaves, branches, dead fish, foam, and horse manure. No waste pollution or cercaria dermatitis was confirmed.

Risks

Cyanobacteria blooms have occurred annually from 2017 onwards, with bans issued in 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024, and 2025. Diffuse pollution sources include direct shore pollution and discharge from municipalities without treatment, as well as communal water discharge from a cottage area into groundwater infiltration systems. Microbiological pollution from diffuse sources presents catastrophic impact with near-certain probability of effects (extreme risk). Phosphorus discharge from diffuse sources presents small impact with less probable effects (medium risk).