"There's currently just under ten centimetres of water at my berth," says Heinz Stärk. He usually moors his Dehlya 25 with the keel raised at the jetty off Iznang. But even the draught of just 35 centimetres has been too much since last week. Stärk recently took his boat out of the water.
And more and more sailors on Lake Constance are feeling the same way. "We have a Jeanneau 2000 especially for low water levels at our buoy site on Untersee," says Annette Bernauer. Together with her husband Klaus Dietzel, she was already worried that their small cruiser might get stuck on the buoy stone. Now they have also put their boat ashore. Just in time. Because even under the crane, the water is already too shallow here and there.
The Constance gauge on the upper reaches of Lake Constance dries towards a summer low ( YACHT reported >> ). The records go back more than 150 years. On the smaller Untersee, the water level had already fallen below the previous minimum mark in July. Despite regulation, water levels on the Ammersee and Starnbergersee are also currently significantly lower than usual. However, harbours, buoy sites and slipways are often dependent on the higher water levels.
Michael Hermann, harbour master at Bodensee-Yachtclub Überlingen, has so far only experienced draught problems on guest moorings. But even for him, pleasure craft operations are restricted. "The seaweed is growing so much this year; after three weeks, boats were no longer able to get out of the harbour under their own power." As a result, "Erna", a special boat that mows the plants down to a depth of two metres, is on permanent duty on the Obersee.
Lots of seaweed also causes problems
"The strong growth of seaweed is actually a sign of good water quality," Dr Harald Hetzenauer, Head of the Institute for Lake Research in Langenargen, explains the findings to "Yacht". "From a biological point of view, it should be removed as little as possible, as fish like to breed in it. Even when the boats come in and out." That's why he only recommends selective mowing at most. "We also have more seaweed in the Constance funnel, which reduces the outflow," says the scientist. "Otherwise the water level in the upper lake would be even lower."
Carpets of algae several hundred metres wide are developing off the mouth of the Schussen near Eriskirch. "This is due to the phosphates in the water," explains Harald Hetzenauer. "In the 1970s, heavy investment was made in wastewater treatment around Lake Constance with strict guidelines, with success. These algae need CO2, light and nutrients. At the current low water level, a third of the Schussen has already passed through sewage treatment plants and the sewage water still contains some phosphate". This is the reason for the current strong growth. "The problem is not the green algae in the water, but as the water level continues to fall, they dry out and develop foul-smelling foul gas, i.e. hydrogen sulphide or nitrogenous gases". Previous attempts to remove the strong-smelling algae have failed. "Even trapping it with oil booms doesn't work, the algae submerge underneath".
Lake Constance shines like the Caribbean
In contrast to the bright green, the water in Lake Constance is currently a Caribbean turquoise colour because the diatoms are growing particularly strongly. "As they grow, CO2 is extracted from the water, causing calcite to precipitate and reflect the light," says Harald Hetzenauer, explaining the phenomenon. "In principle like in a mountain lake, but there mineral particles in the glacial turbidity provide the refraction."
In recent summers, owners have had to crane out for weeks at a time when water levels have changed. "We are certain that we won't be able to get the boat into the water this year," says Annette Bernauer. "We haven't had any enquiries about lifting keels yet, we supply the special technology but we don't have a shipyard that can implement it on the boat," says Michael Finckh from hydraulics specialist GKS Kressbronn. He is the owner of a 30-metre warping cruiser, a long keeler that could not be converted anyway. "We had our crane appointment on Friday. It would still be enough at the berth, but we can no longer get over the bar at the entrance to the harbour at the Württemberg Yacht Club Friedrichshafen. And it will soon be too shallow under the crane.
"I'm now going out for a swim with my air mattress," says Heinz Stärk, describing his inner water level. Annette Bernauer says with gallows humour: "This summer, we'll be spending more time hiking in the Churfirsten mountains and mountain biking here on the Höri peninsula."
