Fish could die Rising water temperatures threaten fish in the region

Bonn/Region · Water temperatures in regional waters have gone up due to the ongoing heat and this could endanger fish populations. Authorities are warning that fish may die as a result. But even heavy rains could prove harmful.

The constant heat is making it difficult for fish living in lakes and rivers in Bonn and the region because the water temperatures are rising. The NRW Ministry of the Environment has already warned that this is a problem and believes it may be possible that we see fish dying in the area. Water temperatures have reached a critical temperature of 27 degrees Celsius or more, and the sinking oxygen levels in the warmer waters causes stress for the fish. Although there are no signs of fish dying in the rivers of the region at this time, experts are already on alert.

For the Rhine, a water temperature starting at 28 degrees is considered critical for the fish population, according to the State Environmental Bureau (Lanuv). The 28 degree mark is also the border limit of the European Surface Water Ordinance. Because the temperature of the water determines whether power plants may introduce cooling water. On the weekend in Bad Honnef, the water temperature exceeded this limit for a period of time. On Tuesday, the water temperature was 27 degrees. "The temperatures in the Rhine have approached a critical mark," says Lanuv spokesman Wilhelm Deitermann. They are closely observing how it develops.

Important for life in the waters is the oxygen that is dissolved in the water. For fish, the lower limit is four milligrams per liter, for the Rhine, a reading below seven milligrams is considered critical. In the Rhine, the value varies usually between seven and 12 milligrams, on Tuesday at the measuring point in Bad Honnef it was at 9.1 milligrams which is not critical. But that is not a reason for an all-clear. In addition to the heat, heavy rain can also lead to fish mortality if large amounts of dust and mud are flushed into the river.

Even more than the state authorities, the Federal Environmental and Nature Conservation Bureau (BUND) are warning of the rising temperatures in the Rhine and its tributaries. In the near future, the water temperature of 28 degrees could be surpassed, which is dangerous for the ecology of the water. "The predicted extreme temperatures in North Rhine-Westphalia and the further sinking runoff give reason to fear that the Rhine and some of its tributaries will reach the critical limit of 28 degrees in the next few days," says NRW-BUND chairman Holger Sticht. When the water gets to at least 28 degrees, damage to the aquatic biology could be expected. Besides the Rhine, the city of Bonn sees no danger for other bodies of water in the city. An exceptions to this is the lake in the Rheinaue, which is currently being fed with fresh water.

Citizens should not take water from the Sieg

The situation is already problematic at the Sieg River. Normally, 33,000 liters of water per second run through the measuring point in Kaldauen, but now it is 4,000 liters per second. According to state environmental authorities, the water temperature in the Sieg reached more than 28 degrees on the weekend. The environmental office of Rhein-Sieg-County has since reacted and asks that no more water be removed from rivers, streams and ponds. Many citizens use it to irrigate their gardens. Fines are imposed in cases of infringement.

Elsewhere, the situation for animals living in the water has already intensified. In Hamburg, nearly five tons of dead fish were removed from the water and disposed of on the weekend. According to the environmental authorities, it was the heat that caused the mass dying.

(Orig. text: Andreas Dyck, Translation: Carol Kloeppel)

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