A fish restaurant on Lake Chiemsee last week: It’s one of the first really hot days of the year, all the tables are occupied, the waiters carry fish and wine from the kitchen together. At first glance, everything is quite normal. What only becomes apparent after a while: Despite the heat, some of the guests are wearing their sweaters or jackets, some even with hoods on their heads. Guests keep asking if they can move away from the bushes. Others leave their pike-perch and char untouched and seem to flap the air erratically. The reason for all this: mosquitoes. More precisely: swarms of mosquitoes.
Parts of the Chiemsee and many of its places near the shore or water are currently being hit by a plague of waterlogged water like it hasn’t existed in a long time. The suckers buzz not only in restaurants in the evening, they also plague locals and guests in kiosks and seaside resorts during the day.
There is a relatively simple explanation for the annoying phenomenon. This year the mosquitoes were not fought. Some innkeepers grumble behind closed doors that the authorities simply missed the narrow window of time in which the mosquito larvae could have been destroyed. That’s not wrong, but it’s not entirely right either.
The Wastewater and Environment Association (AUV), to which ten municipalities around Lake Chiemsee have joined forces, is responsible for combating mosquitoes. If the mosquito population threatens to become a problem for local residents and guests, the AUV uses the BTI preparation. This agent, which is produced by bacteria, bound in protein and then deployed frozen in ice using a helicopter, is eaten by larvae and kills them. But according to the AUV, that was not possible this year. Because the application of the agent is linked to strict specifications.
The river level of the Alz also plays a role
Quirin Schwaiger is the managing director of the association. He says they shouldn’t deploy BTI until the Alz has reached a certain level. From this one can conclude how extensive areas around the Chiemsee are under water and thus offer good conditions for mosquitoes. However, BTI is never used over the lake and in the nature reserve around the mouth of the Tiroler Ache.
But this calculation was messed up by the heavy rain in May: “The water level had not yet been reached. But the areas that are crucial for the eggs were already so wet and saturated from the constant rain that the mosquitoes were already in a developmental stage , in which we can no longer fight.” The insects only absorb BTI for a certain period of time on their way from larvae to mosquitoes, after which the agent is basically useless.
Since 2002, mosquitoes at Lake Chiemsee have been combated. According to Schwaiger, the AUV was not allowed to use the water level BTI until three times. It’s just stupid that two of the three cases were in 2021 and 2022. The water level has not been high enough in the past two years due to the drought. Although no areas were flooded either, the high incidence of mosquitoes this year is still due to the past two years, says Schwaiger. Mosquito eggs can survive for several years. In addition, there was hardly any ground frost last winter. Good conditions for the reproduction of insects.
“Four guests left because of the mosquitoes”
“We asked our communities whether the mosquitoes had an impact on tourists. Four guests left because of the mosquitoes,” says Schwaiger. A manageable number. According to the tourism association of the city and district of Rosenheim, it has not yet received any complaints from visitors. “But it is also clear that the burden on the population and tourists is still high,” says Managing Director Schwaiger.
However, there is also good news: the female mosquito has a life expectancy of around 50 days. According to Schwaiger, the population that was triggered by the first flood in May may have died out by early to mid-July. In other words: from the beginning of July he expects the situation to ease significantly.