Fish

In August 2022, the massive bloom of the toxic brackish water algae Prymnesium parvum in the Oder River led to the largest fish kill to date along more than 300 kilometres of river. More than 260 tons of dead fish were collected and around 1,000 tons of fish of all species died in total. Sub-project 11 "Fish" assesses the damage for individual fish species and records the recovery of the stocks in the Oder and the connected floodplain waters. 

Twice a year, in spring and autumn, the project staff use electrofishing to record the adult fish in ten sample stretches each in the main stream of the border river and in ten permanently connected and ten temporarily isolated floodplain waters. The sampling stretches are evenly distributed across the sections of the middle and lower Oder. In addition, the juvenile fish population is determined in six river sections at the end of July each year. In each section, the main habitats, bank structures and floodplain waters are surveyed using electrofishing specially adapted to juvenile fish.

Our project partners from the Institute of Inland Fisheries Potsdam-Sacrow are also analysing catch data from commercial fisheries from the period before and after the disaster and are scientifically supervising the fisheries monitoring by fishing companies on the Oder. Due to their marketing interests, commercial fishermen use other fishing methods that favour species and size classes that are systematically underrepresented in standard monitoring methods. Monitoring of commercial fisheries is therefore an important addition to assessing fishing damage and the recovery of fisheries.

The IGB has been analysing fish populations in the Lower Oder since 1998 and in the entire border river and the Lausitzer Neiße, the largest tributary of the Oder, since 2006. As a result, extensive data on population densities and trends are available for all fish species in the Oder, which serve as references for the changes caused by the disaster and the recovery of the populations.