Weather Conditions: Dead Fish in the "Dechsi"

The combination of

• prolonged heat
• a lack of rainfall and
• maximum water temperatures of up to 32 degrees Celsius

. The Office for Environmental Protection and Energy Issues has drawn attention to this.

Heat stress combined with low oxygen levels leads to fish deaths

Longer and more intense heat waves cause lakes and ponds to warm up more significantly, leading to a drop in the oxygen content of the water. Such extreme weather events significantly increase the risk of fish mortality and, according to current scientific findings, are expected to occur more frequently in the future. A lack of rainfall and sharp temperature swings following heavy rain events also contribute to further exacerbating the situation.

Do not feed waterfowl

Further fish kills cannot therefore be ruled out. Countermeasures include ecologically balanced water management and the reduction of nutrient inputs. Reason: Excessive nutrient inputs promote algal blooms, which can further strain the oxygen balance. The public can help by refraining from feeding waterfowl, as food scraps and increased droppings in the water raise nutrient levels.

Dead Dwarf Catfish

Since early May, there has been an increase in dead dwarf catfish at Dechsendorfer Weiher. This is due to a disease affecting this fish species. There is no danger to humans or other animals; the fungus affects only dwarf catfish.

This species is problematic in many European bodies of water because it is not native and reproduces very rapidly. The dwarf catfish competes with native fish species. It displaces juvenile fish and harms the populations of other species. Furthermore, dwarf catfish are predators that feed on fish eggs, insect larvae, and small fish.

Due to their high adaptability, they survive even under unfavorable conditions such as low oxygen levels or turbid water, allowing them to spread rapidly. Since they often lack natural predators in these waters, their populations can grow significantly. Overall, dwarf catfish thus contribute to disrupting the ecological balance of water bodies. The Dechsendorfer Weiher is also struggling with this species. Due to the high population density, the Animal Health Service diagnosed a disease (fungus) in dead dwarf catfish in 2024, which leads to the death of the affected fish.

Staff members are regularly on site to remove dead fish.

Photo: Environmental Agency—a small, dark fish with barbels.