The death of hundreds of thousands of fish in the River Oder this summer was most probably caused by the excessive growth of an alga that flourishes in brackish water, German environmental authorities said in a report issued on Friday.

The report by a team led by the German Environment Agency (UBA) concluded that the alga Prymnesium parvum, which releases toxins into the water it grows in, led to the mass killing of fish.

The conditions for such an algal bloom were present in the river in summer, the experts said, with the concentration of salt in the water the "primary trigger."

The conclusions reached by German authorities largely match those of Polish ones. The latter also identified algal bloom as the cause of the fish deaths while, however, ruling out contamination by polluted water from industry as being behind the deaths.

What did the report say?

The experts said they could not determine the exact source of the high salinity in the river's water.

"The sources of the salts, other elements and chemicals are unclear," their report said, adding that "multicausal mechanisms" had triggered the fish deaths.

According to the report, high summer temperatures and a paucity of rain had aggravated the situation by increasing the concentration of harmful substances in the water. 

Although the German team of experts  did find herbicides in the water that "very probably" stemmed from industry, they said the acute fish poisonings could not be attributed to these substances.

The report recommended carrying out further research on the spread of the alga in question and improving the cross-border warning system to help prevent catastrophes of this kind in the future. It also said that current limits on dumping substances into bodies of water should be scrutinized.

The mass fish deaths were first discovered on the German side of the river on August 9. As, according to government information, Polish authorities already knew of the disaster by the end of July, Germany has criticized Poland for not reporting it earlier.

 What have environmentalists said?

Greenpeace pinned the blame for the high salinity of the Oder's water on the Polish mining industry, citing analyses by four of its activists.

"We call on the Polish and German governments to renature the river in future, to watch over it round the clock and to ban the introduction of harmful substances such as salts and heavy metals," said Greenpeace spokeswoman Nina Noelle.

Friends of the Earth (BUND) pointed out the likely role of climate change in the catastrophe and called for long-term measures to preserve the river's health.

"The mixture of low water levels, high termperatures and the growth of the salinity-tolerant alga can reoccur in the Oder or in other rivers as well next summer," it said.

"This means it is more urgent than ever to have cross-border cooperation on river management and a stop to all regulation measures," it added.

The Polish and German governments are planning to undertake joint measures to develop the river, among other things, to create stable traffic conditions for shipping. The plans have been condemned by many environmental groups from both countries as being harmful to the river environment.

tj/sms (dpa, AFP)

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