Dead fish in the Wkra. What caused the ecological crisis?

Last week, in several towns along the Wkra River, an unusual discoloration of the water and the presence of dead fish were observed. After meetings of the crisis management team of the Mazovian Voivodeship, intensive aeration of the river was launched. What is the situation today?

Sensational headlines versus data

Some media reported that as much as 2–3 tons of dead fish could be found along a 100-kilometer stretch of the Wkra. The Regional Water Management Authority (RZGW) in Warsaw firmly denied this information, clarifying that as of yesterday, 900 kg of fish of various species had been removed from the water. Final data on the losses will only be available once operations on the river are completed.

The first reports of fish die-off came from the town of Nidzica and the area around Działdowo, where the water is now clear, and the fish appear to be in good condition. As the RZGW in Warsaw explains, the pollution moved downstream over several days toward Żuromin, Lubowidz, and Siemiątkowo, and then further to Drzazga, Radzanów, and Strzegowo. Later today, crisis management meetings will also take place in Mława and Ciechanów counties.

Since last Friday, a ban on swimming and using the Wkra has been in place, including watering animals. The river section from Nidzica to Płońsk is under constant monitoring by field patrols.

Intensive water aeration as a countermeasure

The crisis in the Wkra has been addressed by Wody Polskie (Polish Waters) in cooperation with the Mazovian Voivode, the Volunteer Fire Brigade, and the Ciechanów branch of the Polish Angling Association. The main remedial actions involved deploying six aerators to oxygenate the water, improving conditions for ichthyofauna. The devices are moved downstream as the pollution spreads. In addition, the RZGW in Warsaw reports regulating water flow through discharges from small hydroelectric power plants and the use of damming devices.

Volunteers from riverside towns also joined the rescue effort, collecting dead fish from the river. The owners of the agritourism farm Dworek nad Wkrą organized pools into which live fish were transferred and supported with additional oxygenation.

The trail leads to peat bogs

The first findings of the agencies coordinating the situation suggest that the massive fish die-off was caused by a lack of oxygen. The Provincial Inspectorate for Environmental Protection in Olsztyn has ruled out the possibility of sewage contamination. However, the question remains: what deprived the Wkra of vital oxygen?

The most likely scenario is the runoff of water from nearby peat bogs following heavy rainfall that hit Mazovia two weeks ago. Along with the water, humic substances entered the riverbed, giving the river a dark coloration. Their decomposition in the aquatic environment involves high oxygen consumption, which may have led to the mass fish die-off. Final confirmation of this theory is still pending. The Provincial Inspectorate for Environmental Protection in Warsaw has collected water samples and is conducting analyses.

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main photo: Zofia Leszczyńska-Niziołek