Vn Sedlice

Czechia River 1 - Excellent

VN Sedlice is a reservoir serving as a pre-reservoir to trap pollution from its catchment before water enters the Švihov water supply reservoir. The bathing area has a grassy bank with a sloping bottom and a beach length of 100 metres. Visitor numbers are below 100 annually. The reservoir is highly eutrophic with regular cyanobacteria blooms and exhibits significant seasonal variability in water quality depending on flow rates.

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Water

A man-made reservoir (pre-reservoir) with a surface area of 38 hectares and elevation of 448 metres above sea level. The dam depth is 13.7 metres. Average theoretical water retention time is 11 days in summer but varies with seasonal flows. Specific runoff is 6.26 litres per second per square kilometre with average discharge of 2.58 cubic metres per second. The water body serves the broader Želivka-VN Sedlice catchment area of 411.61 square kilometres.

Location

The bathing spot is located at VN Sedlice reservoir. A refreshment stand and toilets are available at the site.

Facilities

Refreshment stand, toilets.

Season

June to August.

Water Quality

Microbiological quality is classified as excellent. The reservoir exhibits highly eutrophic conditions with high phytoplankton development. Phytoplankton biomass is highly variable seasonally, frequently exceeding the 50 micrograms per litre limit, with maximum recorded values of 520 micrograms per litre chlorophyll-a on 26 September 2024. Cyanobacteria of genera Aphanizomenon and Microcystis are permanent components of algal blooms. Water pH is typically elevated as a result of phytoplankton photosynthesis. Water transparency ranges widely from 1.5–2.5 metres during clear water periods to 0.2–0.5 metres during strong phytoplankton development. Overall assessment ratings during the swimming season (June–August) were 2.3 and 2.4 in favourable years (2020, 2023) and 4.4–4.5 in unfavourable seasons (2022, 2024), with approximately half of assessments in poor years rated at level 5.

Risks

During flood discharge periods, influx of erosion material, nutrients, and potential microbiological contamination occurs. The reservoir is permanently eutrophic with toxicologically risky cyanobacteria capable of forming dominant components of the phytoplankton community. Water transparency and pH regularly exceed limit values for bathing waters.