Břevnická Nádrž

Czechia River 1 - Excellent

Břevnická nádrž is a reservoir located at an elevation of 526 metres with a surface area of 12.5 hectares. The water body has a maximum depth of 6 metres at the dam and an average theoretical water retention time of 57 days at an average depth of 2 metres, or 86 days at 3 metres depth. The reservoir exhibits eutrophic characteristics with elevated algal and cyanobacterial biomass, though phosphorus concentrations are not exceptionally high.

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Water

Reservoir with a surface area of 12.5 hectares, maximum depth of 6 metres at the dam, and an average water flow rate (Q) of 0.050 m³/s. Specific runoff (q) is 8.42 litres per second per square kilometre. The water has a grassy beach with a length of 500 metres and muddy bottom.

Location

Břevnická nádrž is located in the Vysočina region of the Czech Republic. A nearby settlement, Dobkov, is present on the shoreline with recreational buildings.

Facilities

The bathing site has no operator and no facilities.

Water Quality

Monitoring was conducted until 2013; the bathing site was not monitored from 2014 to 2015. The last assessment in 2013–2016 indicated excellent water quality, but cannot be classified due to lack of recent data. During 2016–2019, water quality assessment indicated impaired quality with microbial contamination. Cyanobacteria with toxicological risk were particularly prevalent in August, with maximum cell counts exceeding 100,000 cells per millilitre in 2018. Total phytoplankton biomass exceeded the 50 µg/litre chlorophyll-a limit seven times between 2016–2018, with an absolute maximum of 150 µg/litre. Phosphorus monitoring was not conducted during 2016–2019; previous monitoring from 2009–2011 recorded relatively low concentrations near 0.05 mg/litre. Water pH ranges from 7.1 to 10.7. Transparency falls below 1 metre only in certain years (2016, 2018, 2019), with a minimum of 0.6 metres in August 2016. No short-term pollution was detected.

Risks

Cyanobacteria blooms occur regularly, with toxicologically risky species prominent particularly in August. Diffuse pollution sources include upstream fish ponds with high risk for phosphorus input, the settlement of Dobkov and recreational buildings on the shoreline with extreme risk for phosphorus input (particularly during heavy rainfall events), and fish stocking of the reservoir itself with high phosphorus risk. Low microbial contamination risk is associated with upstream ponds and fish stocking, while medium microbial contamination risk is associated with the Dobkov settlement and recreational buildings.