Mass fish deaths due to heavy rainfall

In several parts of the country, many fish have been found dead due to the effects of the heavy rains that fell, especially on Thursday. Water authorities have been receiving dozens of reports of dead fish since Friday. Authority staff is working hard to remove the dead fish as quickly as possible, as it is already getting hot again, water board Hoogheemraadschap Hollands Noorderkwartier said.

The fish are dying due to lack of oxygen, the water board said. The rains have caused the sewers to overflow. As a result, dirty water is entering ditches, ponds, and rivers. The rains have also washed road dirt and dog feces into the water. Water pollution causes the oxygen level in the water to drop very quickly. The fish then literally gasp for air and die if the water is not oxygenated.

Especially the bigger fish, which need more oxygen, crave air, according to the water board. Sometimes the fish remain at the water surface in a kind of suspended state. In this state, they put themselves in a passive state so that they need as little oxygen as possible. Later, they swim again. Accordingly, not every fish that stops moving is automatically dead. Nevertheless, unfortunately, many hundreds of fish have not survived, the water board reported.

Blue-green algae and botulism also quickly develop in low-oxygen and warming water. The Rijn en IJssel Water Board has therefore placed two aerators in the Ahauser Aa on the border of Twente and Germany, which pump extra oxygen into the water. Further on in the Netherlands, the Ahauser Aa is called the Schipbeek, which flows past Deventer, among other places.

Water boards ask people who see dead fish floating in the water to report it. It is not intended that people take the fish out of the water themselves, as this should be done professionally, the water board stressed.