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Warm bathing lakes: heat is a health risk for people and fish


The quarry lake is very popular - high temperatures stress people and fish

There is hardly anything better than the cool sweaty heat wave than cooling off in a swimming lake. However, the extreme temperatures often cause a relatively high water temperature. This not only affects refreshment for us humans, but also troubles the fish.

Refreshment in the swimming lake

In order to stay cool in the current heat, it is advisable to visit the nearest swimming lake. But in some places, the dredging lakes and other inland waters are so warm due to the high temperatures that they hardly bring any refreshment. And even water temperatures that we find pleasant can be fatal to fish because the oxygen content in the water decreases with increasing temperatures. The Leibniz Institute for Freshwater Ecology and Inland Fisheries (ITUC) has announced this in a communication.

Inland waters are more important for recreation than the sea

People can relax best in nature. The water in particular has a strong attraction for us. This also applies to lakes and rivers.

According to the IGB, a survey carried out together with the Humboldt University in Berlin (HU) showed that two thirds of Germans spend at least once a year on inland waters to go jogging or walking.

Around half swim or bathe regularly in a lake or river or use the shore for sunbathing.

"And around a third of the population in Germany is in the water to enjoy the animals and plants," explains study leader Prof. Dr. Robert Arlinghaus from the IGB and the HU a reason for the importance of inland waters for the recreation of people.

According to a recent survey in Lower Saxony by the Technical University of Berlin (TU), inland waters are even more important for local recreation than the sea.

Little is known about the recreational significance of smaller quarry ponds. That is now changing due to the research work in the BAGGERSEE project, which is being worked on by scientists from IGB, HU, TU and the Lower Saxony Angler Association.

First results show how widespread the type of water is like an excavated lake. In terms of area, around 70 percent of all lakes in Lower Saxony are excavation waters or quarry ponds. Lower Saxony alone has over 30,000 artificial stagnant waters.

"Because of their widespread use, quarry ponds are of great social importance for local recreation," said BAGGERSEE coordinator Prof. Robert Arlinghaus.

Optimize local recreational value of dredging lakes

However, with the current record heat there are also losers at the quarry lake:

Large amounts of algae can occur in waters that are heavily polluted by agricultural and other nutrient inputs. These make a stay in the water a dangerous bathing fun for people, as skin reactions threaten.

For fish and other water dwellers, the high amounts of algae that cause the oxygen in the water to become less can be life-threatening.

The BAGGERSEE project now wants to optimize the biodiversity - and thus also the praised local recreational value - of quarry ponds.

For example, the introduction of dead wood and the creation of shallow water zones in the steeply falling quarry ponds are intended to increase the occurrence of fish, amphibians and dragonflies.

Humans also benefit from good structural diversity on the water and from developing the quarry ponds close to nature. (ad)

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