Just a few days of summer heat are now enough to cause the water level of the shallow lake to drop to critical levels and bring the real problem to light: the mud. And not just around the jetties and in the shore areas. Mud islands are also forming in the middle of the lake. "Just three weeks ago, a sailor touched down on a mud island during a regatta," reports Ernst Greten, Chairman of the Verein zum Erhalt des Steinhuder Meers (VESM). "If this continues, we will no longer be able to organise fair regattas here. A disaster for sailing in the region."
The Wettfahrtvereinigung Steinhuder Meer organises around 40 regattas every year, including regular German and European championships. The importance of the area for the regional identity and economy can hardly be overestimated. The association is therefore committed to restoring the old current conditions that prevailed in the 1960s and putting a stop to the deterioration. To achieve this, the sand barrier in the Deipen would have to be removed and the silted-up deeper areas would have to be cleared of mud in a timely manner, according to the association's demands.
Researching the causes: What do the dips have to do with it?
The Leine once ran through the Steinhuder Meer, creating deep channels known as "Deipen". The prevailing westerly wind drove the swirling mud to the east, which was then transported westwards again by the undercurrent in the three metre deep deips. This caused the Steinhuder Meer to shift from west to east over the last 10,000 years. But now everything indicates that a man-made sandbank has formed. "There has always been mud," explains Greten, "but only to the west of Wilhelmstein. When we sailed here in the 1960s/70s, there were still waves to the east. At some point, they became less and less. A depth measurement in 2019 showed that the dips have silted up and the water can no longer drain away."
The current in the Deipen, which has been eliminated by the sandbank, can no longer sufficiently break down organic matter. As a result, there is a significantly higher level of sludge formation than before. Pumping measures within the sea are thought to be a possible cause of the sandbank. The shore current is also impeded, so that more deposits form there. In short: the lack of current leads to more mud.
Another assumption for the increasing sludge was algae due to inputs from agriculture. Ernst Greten comments: "Unlike the Dümmer, for example, there is no significant input from agriculture in the Steinhuder Meer because there is hardly any neighbouring agriculture and no tributary. Apart from that, the algae are also an advantage for water sports on the Steinhuder Meer because they keep the water turbid and fewer aquatic plants grow in turbid water." Around the turn of the millennium, there was less algae for a few years and the water suddenly became completely clear - initially to everyone's delight. But then came the narrow-leaved waterweed. It multiplied explosively. Half the lake was covered with an almost closed green carpet that made sailing impossible.
The effects of the sludge
Due to the lack of undercurrent, the sea is silting up from the centre and much faster than before. When the water levels are low in summer, as they are now, the mud becomes visible. "In the short to medium term, we will lose the Steinhuder Meer as a cultural asset and economic factor for tourism, leisure, sport, nature conservation, fishing and as an ecological biotope," says the association on its website. Not only recreational sailors are affected, but also commercial providers of excursion trips, which are an important part of the tourist infrastructure. In the bay south-east of the bathing island, several jetties have already silted up and become unusable due to siltation. In addition, the water level has been falling for years during hot spells. In July 2025, a level of just 93 centimetres was measured at the Wilhelmstein gauge - around 30 centimetres below the target value. The situation was even more dramatic in 2018, when the water level dropped by almost 50 centimetres. Captains of excursion boats, skippers and jetty owners are despairing at the situation, which is jeopardising the entire season - and just before the traditional peak "Steinhuder Meer in flames", which is scheduled for this weekend (22 to 24 August 2025).
Proposed solutions
Although the water is pumped out every year, around 40 thousand cubic metres is far too little, says Greten. This would actually just about eliminate the annual effects and only selectively around the footbridges. This would cost an unnecessary amount of money over many years and would be a battle against windmills. "In order to save the Steinhuder Meer in the long term, around five to eight million cubic metres have to be pumped out, even from the deeper areas." But where to put all the sludge?
The VESM proposes an area of moorland adjacent to the Steinhuder Meer as a storage area. "Of course, we would never suggest using an intact moor as a storage area," says Greten. "But peat is still being extracted here. The moor is broken. The sludge could be pumped into the holes created in the peat polder. Tests have shown that the bog plants thrive on the mud." The area could be renaturalised, killing two birds with one stone, so to speak. The area of the moor is around 20 square kilometres, but only around 0.5 to one square kilometre would be needed. No trees would have to be felled and no land would be used, which would reduce the desilting costs. The filled polder can grow very quickly, produces oxygen and is good for the climate. The peat-filled area would be surrounded by dams and any heavy metals would not be washed out. Saving the sea could also be subsidised by the EU, the association suggests. A large panel discussion with all stakeholders is planned on stage on 9 October. This could decide whether sailing has a future on the Steinhuder Meer.
