After the hot days in August, there was at least some precipitation and temperatures below 30 degrees. The short break was good for the Main. The water experts of the government of Lower Franconia remain vigilant and “with the utmost attention”, says Axel Bauer, who is responsible for water management. The “warning” for the reporting area between Kahl am Main and Würzburg, which has been in effect since August 13, will initially be upheld. “From an ecological point of view, the Main and the other bodies of water in Lower Franconia are far from over the mountain this summer.
“Main alarm plan” early warning system
The currently valid warning is the second highest of three levels of the “Main Alarm Plan”, which the government of Lower Franconia installed in 2015. The “alarm plan” is an early warning system that is supposed to indicate when it becomes critical for the water ecology of the Main, for example with regard to the water temperature or the oxygen content. According to Axel Bauer, the more moderate temperatures of the past few days have also affected the water temperature of the Main. For example, on Sunday, August 16, the maximum temperature of the Main water near Würzburg was 25.8 degrees: Still a high value, but it means a certain relaxation.
“Last week in the Main we sometimes had values above 27 degrees, which is really severe. The greatest burden for the Main is simply the weather, these are the high temperatures Main to minimize. ” Axel Bauer, Head of Water Management Government for Lower Franconia
This should be done using the “Main Alarm Plan”. Although the alarm plan cannot pronounce legally binding usage bans, it does give instructions to the authorities or so-called dischargers into the Main: industrial companies, power plants or sewage treatment plants that should avoid additional pollution of the Main at the “Warning” and “Alarm” levels, i.e. discharges of wastewater, Mud clearance or dredging.
Oxygen content in the Main threatens to decrease
Axel Bauer is currently paying particular attention to the oxygen content in the Main. One reason is that there is a slight algae bloom on the Main near Erlabrunn. When these algae die, the oxygen content could be reduced within a short period of time. “We will be observing this very critically,” said Axel Bauer. However, the water expert from the government of Lower Franconia does not currently fear fish deaths in the Main.
Late summer is a tricky phase for the river and fish
This is also the opinion of Wolfgang Silkenat, the fisheries advisor for the district of Lower Franconia. “We have the advantage in the Main that fresh water is constantly flowing into the Main through the tributaries from the tributaries and especially from the Danube. Let’s hope it stays that way,” said Silkenat. Currently about a third of the water in the Main comes from the Danube. “Otherwise we would probably already have dead fish in the Main,” says Silkenat. The all-clear for the coming weeks could not yet be given. The second half of August and the first half of September are particularly decisive here.
Fish die in quarry ponds due to lack of oxygen
In the case of great heat and at the same time shorter days, there would be the risk that too little oxygen could be formed during the day, which is no longer sufficient at night. This could then lead to problems, especially at quarry ponds such as in the Haßfurt area. “In the past few years we have had terrible fish deaths here because the quarry ponds had overturned due to a lack of oxygen,” says Silkenat.
No restrictions for swimmers
The experts consider the influence of swimmers in the Main to be of secondary importance, who are looking for a particularly large number of people to relax on and in the river this year. It is true that swimmers, for example through sunscreen, “bring substances into the Main that are not necessarily good for the river,” said Axel Bauer from the government of Lower Franconia. Ultimately, however, given the amount of water in the Main, this does not matter. Bathing bans were therefore not threatened, even if the heat continued.
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