Researchers suspect a combined effect of algae and environmental toxins or a chain reaction caused by an unknown emission source.
The number of golden algae has exploded
None of them, at least so far, have been shown to be the source of the toxins that caused the fish deaths. The authorities are still examining about 60 pipes in more detail.
Instead, satellite images have revealed that there have been larger than usual amounts of leafy green in the river in recent weeks, which in turn indicates an abundant presence of golden algae.
Golden algae produce toxins that can kill fish. It also reduces the oxygen content of the water.
Higher than usual amounts of pesticides have also been found in the water, and it has been saltier than normal.
Chemical cocktail or chain reaction
The German Environment Ministry believes that the fish deaths were caused by a combination of several substances.
– According to our research so far, none of these substances have killed fish on their own, the spokesperson of the ministry Andreas Kübler said in an interview with Euronews.
According to the BBC, some scientists suspect a chain reaction in which some pollutant has increased the salinity of the river, increasing the algae to lethal levels.
Europe’s record hot and dry conditions could have made the situation even worse, and climate change has intensified heat waves.
Fish may also die in the future
Both Polish and German authorities have admitted mistakes in handling the case. They reacted to the situation slowly and argued about the results of the measurements.
A Polish researcher interviewed by the BBC Andrzej Kapusta fears that fish deaths will continue in the future, especially if the cause of the disaster remains obscure.
– We need an accurate and online monitoring system that transmits information to the authorities faster, says Kapusta, according to the BBC.