Four years after Oder disaster, fish stocks rebound but mussels languish, leaving river vulnerable
Four years after one of Europe’s worst river die-offs, fish have returned to the German-Polish border river, but critical freshwater mussels have barely recovered, leaving the ecosystem fragile and at risk of another toxic algal bloom.
The 2022 catastrophe
In August 2022, a combination of high salinity, low water, heat and a bloom of the toxic golden alga (Prymnesium parvum) killed an estimated 1,000 tonnes of fish in the Oder, along with large quantities of mussels and water snails. It was one of the most severe riverine mass-deaths in Europe in decades.
Fish rebound faster than mussels
A special investigation led by the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), presented in Schwedt on Monday, finds that many fish species have recovered relatively well over the past two years because they had refuges from which to recolonise. However, large freshwater mussels — the river’s most effective natural filters — remain “massively impaired,” according to the report. Their absence could encourage further algal blooms.
The environmental disaster on the Oder in the summer of 2022 showed how vulnerable our waters and floodplains are. We should do everything we can to ensure that such an event does not repeat itself — here or in other rivers.
Salt still flowing from Polish mines
The scientists point to ongoing saline discharges from Polish coal and copper mining as a central cause of the golden alga proliferation. So long as this practice continues, the report warns, another catastrophe remains possible. German environment minister Carsten Schneider (SPD) said he is in talks with Poland about the salt loads and that Warsaw is examining measures to reduce the inflows.
Long road to full regeneration
Fish stocks are projected to recover fully by 2027, but fishery yields will only normalise once larger fish have matured — a timeline stretching several more years. The experts recommend a sharp reduction in salinity, restoration of natural floodplains, reconnection of side channels, and dyke relocations to strengthen the river’s resilience against climate-driven low flows and high temperatures.
- An estimated 1,000 tonnes of fish, mussels and snails die in the Oder River following a toxic golden alga bloom.
- Leibniz Institute presents study in Schwedt: fish stocks partly recovered, but large mussels remain massively impaired.
- Experts project fish stocks will have fully recovered, though fishery yields will take longer.
Political tensions over river engineering
An earlier dispute between Germany and Poland over the construction of groynes along the Oder resurfaced in the minister’s remarks. Schneider expressed strong reservations about any further expansion, stating that Berlin plans only maintenance and renaturation measures. Creating retreat spaces for aquatic life, he argued, is vital in the face of increasingly hot summers and prolonged dry spells.
