Lower Silesia bans use of Bóbr River after 15 tonnes of fish die during dam draining

The ban

On 4 July, Lower Silesian Voivode Anna Żabska issued an order prohibiting all use of the Bóbr River along a 30-kilometre stretch from the Pilchowice dam to the Rakowice reservoir. The ban covers entering the water, bathing, watering livestock, amateur and commercial fishing, using water for economic purposes, and operating boats. Violations carry a fine. The Government Centre for Security (RCB) sent an SMS alert to residents of Lwówek County.

Attention! Possible contamination of the Bóbr River, along the Wleń and Lwówek Śląski communes. The water must not be used for recreational, economic purposes or watering animals.

The decision followed microbiological tests by the Sanitary Inspectorate showing the water fails to meet bathing-water standards. The inspectorate recommended declaring it unfit for swimming or any water recreation, warning that contact poses a threat to human life and health.

What caused the fish kill

The contamination stems from a mass fish die-off that began early in the week. By Thursday, services had removed approximately 15 tonnes of dead fish from the reservoir and the river below the dam (one local report put the figure at 21 tonnes). The die-off was triggered by the final stage of draining the Pilchowice reservoir, completed at the end of June. The sudden release of water stirred up sediment, causing severe oxygen depletion, a phenomenon known as "przyducha".

Due to fish spawning, we paused lowering the water level from March to the end of May. Later, at the critical moment when the water was lowest in the reservoir, 40-degree heatwaves hit. It also turned out that the level of sediment in front of the dam was much higher than anticipated.

The dam renovation

The draining was necessary to allow a long-overdue renovation of the early-20th-century Pilchowice dam, owned by Tauron Ekoenergia. The 93-million-zloty project began in January and is expected to take two years. It includes work on the dam crest, spillway cascade, galleries, bottom outlets, and the upstream face. Tauron says the investment is critical for flood protection, especially after the devastating 2024 floods, and that failing to carry it out would be irresponsible.

Dead fish are unfortunately the price we have to pay for the flood safety of Lower Silesia's residents. It should be stressed that regardless of when the water level was lowered, the degree of river siltation in the final phase of emptying the reservoir would have remained at a comparable level.

The company added that all operations were conducted under a water permit and supervised by a team of environmental specialists, including an ichthyologist, herpetologist, phytosociologist, and ornithologist. Tauron has pledged to restock the lake at its own expense once the renovation is complete.

Response and investigation

The Voivode’s office said Friday’s oxygen-level measurements showed improvement over the previous day’s readings. The prosecutor’s office has opened an investigation into the incident. Meanwhile, Tauron reported that the removal of dead fish is largely finished, with only isolated specimens remaining, and that oxygenation equipment has been deployed on the river.