Fish stocks recovering in German-Polish river after 2022 disaster

Three years after a massive fish die-off in the Oder River, which forms a long stretch of the German-Polish border, fish populations are showing signs of recovery, according to a leading expert.

"If nothing else happens, we can expect a full recovery by 2026 or 2027," said Christian Wolter, a fish ecologist at the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin.

Species such as zander and pike are thriving once again in the river, he said.

The environmental disaster in the summer of 2022 was triggered by a toxic combination of high salinity, low water levels, elevated temperatures and toxins produced by the algae Prymnesium parvum, commonly known as golden algae.

According to IGB scientists, the extreme salt content of the Oder enabled the algae to bloom on a massive scale. Researchers estimate that the resulting toxins killed around 1,000 tons of aquatic life, including fish, mussels, and snails.

Fishing activity in the river has largely resumed, though to a lesser degree.

"You can't fish as if nothing had happened," said Lars Dettmann, managing director the Brandenburg-Berlin State Fisheries Association. Professional fishermen continue to operate under restrictions aimed at allowing fish stocks to fully regenerate, he noted.

Environmental groups remain concerned about the risk of another mass die-off, especially if salinity levels rise again.

However, increased growth of the algae has not been detected in the Oder river at present, said fish ecologist Wolter, calling it a "very positive" sign.