# Czech reservoirs face deteriorating water quality and bans

> Live situation record from CLSTR: https://clstr.news/situations/czech-water-quality-and-swimming-safety
> Updated: 2026-08-20T10:04:05.000Z. Sources: 15. Developments: 4.

Czech water bodies are trending toward cleaner conditions overall, yet localized deteriorations and recurring cyanobacterial blooms keep authorities alert. While many sites—such as Radava, Hejtman, Staňkovský ponds, and beaches on the Lipno Reservoir—maintain excellent or good ratings, several major reservoirs have faced significant declines.

By mid-August 2026, conditions at the Plumlov Reservoir near Prostějov worsened significantly. After previously dropping to level 3, the water quality reached the highest risk level (level 5) due to high concentrations of cyanobacteria. This has resulted in a strict swimming prohibition, as exposure can cause skin rashes, eye irritation, or gastrointestinal issues. Hygienists have increased sampling to every 14 days, noting that phosphorus runoff and warm weather typically exacerbate quality issues in midsummer.

In South Bohemia, the Orlík Reservoir’s Podolsko area previously triggered a temporary bathing ban with a level 5 rating. Meanwhile, the South Moravian Region faces widespread concerns: the lagoons of the Nové Mlýny and Letovice-Vranová reservoirs have been rated at level 4, failing to meet hygienic requirements and posing risks to children, pregnant women, and the immunocompromised. The Brno Reservoir has also reached level 3. Experts attribute these deteriorating conditions to warm weather and droughts, which promote cyanobacteria growth and reduce water flow.

## Timeline

### 2026-08-20: Water quality warnings and swimming bans issued at Czech reservoirs

Czech health officials have issued swimming bans and warnings at several reservoirs, including Plumlov and Brno, due to poor water quality and cyanobacteria risks.

6 sources. https://clstr.news/cluster/water-quality-warnings-and-swimming-bans-issued-at-czech-reservoirs

### 2026-08-07: Czech reservoirs face deteriorating water quality and swimming bans

Plumlov reservoir’s water quality dropped to level 3, prompting health warnings, while Podolsko on the Orlík Reservoir was rated level 5, keeping a swimming ban in place; other Czech sites remain safe.

4 sources. https://clstr.news/cluster/czech-reservoirs-face-deteriorating-water-quality-and-swimming-bans

### 2026-07-24: Czech rivers become cleaner, prompting families to swim while experts caution on child safety gear

Czech river water quality has improved, drawing families to swim, while experts advise against inflatable sleeves and rings for kids, recommending safer foam straps.

2 sources. https://clstr.news/cluster/czech-rivers-become-cleaner-prompting-families-to-swim-while-experts-caution-on-child-safety-gear

### 2026-07-24: Plumlov Reservoir water deemed safe for swimming despite downgraded quality rating

Czech health officials say Plumlov Reservoir remains safe for swimming, though water clarity fell and chlorophyll‑a rose, prompting a lower safety rating but no health risk.

4 sources. https://clstr.news/cluster/plumlov-reservoir-water-deemed-safe-for-swimming-despite-downgraded-quality-rating

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Cite as: Czech reservoirs face deteriorating water quality and bans. CLSTR, https://clstr.news/situations/czech-water-quality-and-swimming-safety