Aquatic plants on Lake Baldeney: Ruhrverband christens new mowing boat "Kaiman"

On Wednesday, 16 July, a new mowing boat was christened "Kaiman" in Scheppen harbour to better combat elodea. Together with another boat that has been in use for some time, it will tackle the aquatic plants in Lake Baldeney. In addition to Essen's Lord Mayor Thomas Kufen and the Chairman of the Board of the Ruhrverband Prof Christoph Donner, lake manager Boris Orlowski, Managing Director of the White Fleet, and Hans-Walter Fink, Chairman of IG Baldeney, also took part in the naming ceremony.

In the Ruhr catchment area, there are now many invasive species on land and in the water, such as the voracious blackmouth goby and the quagga mussel. And of course the aquatic plant Elodea, originally from North America, which has been known in our region for some time. Although it is harmless in terms of water ecology, it has a massive impact on water sports. The fact that it feels so at home in the Ruhr reservoirs is mainly due to the high water quality, as the Ruhr has become cleaner and cleaner over the past few decades thanks to the Ruhrverband's wastewater treatment plants.

Christoph Donner explains why the new mowing boat is called "Caiman": "We came up with this idea to draw attention to the changes to our ecosystems caused by invasive species. After all, caimans are not native to this area and are also carnivores. Our caiman has specialised in aquatic plants with a big appetite and sharp teeth."

The City of Essen, Ruhrverband, Weiße Flotte and IG Baldeney have been working closely together for several years now, with the division of labour contractually agreed: Ruhrverband procures the boats and provides them in working order. The city of Essen, via the Weiße Flotte, ensures that the boats are manned and that the disturbing aquatic plants (especially the elodea) are mowed. IG Baldeney, which represents the interests of the clubs based on the lake, decides in consultation with the Weiße Flotte which areas of the lake need to be mowed and when. In addition to the mowing boats, as in the previous year, a loading barge from the Düsseldorf district government is also available. It enables mobile unloading directly on the water, shortens the distances for unloading and thus significantly increases the efficiency of the mowing work. These measures are intended to ensure the best possible organisation of sports competitions as well as training operations and recreational use.

"Lake Baldeney is not only an important leisure and recreation centre for the people of Essen - and beyond. It is also a sporting area for many local clubs with different types of water sports. Regular mowing is important so that the sport and the well-known and popular tournaments and regattas can take place here. The support provided by another mowing boat is therefore good news," says Lord Mayor Thomas Kufen.

"We can see in many places how invasive species are changing our environment," says Christoph Donner. "Elodea is a good example: on the one hand, it forms a kind of underwater forest that provides food and shelter for many aquatic creatures. On the other hand, we have to reduce this huge amount of plant biomass if we want to continue to allow recreational use of the Ruhr reservoirs. This is cost-intensive, but a social compromise."

And this is the current situation with aquatic plants on Lake Baldeney: The first test runs took place this season on 16 June following indications from the clubs on the southern shore of increased Elodea growth, although the yield was still very low both during this first test and the next attempt on 25 June. During the third mowing trip on 2 July, specific areas of the bank and harbour as well as access points to the shipping lane along the north bank and areas with known vegetation or possible restrictions on use were included. No massive weed infestation was detected; just four boatloads of elodea had to be mowed down and disposed of.

The situation on Lake Baldeney is therefore still comparatively relaxed, but those responsible explained at the boat launch that the mass growth of elodea could start at any time given the current favourable conditions (lots of sunshine, high temperatures and low water turbidity). "And if that happens, we will be prepared," emphasised Christoph Donner. Then there will be plenty to do, because the elodea grows up to 20 centimetres a day.

Looking back:

In the summer of 2024 - after several consecutive years of weak growth - there was once again a very strong development of aquatic plants on the Ruhr reservoirs. In total, more than 510 tonnes of mowed material accumulated on Lake Baldeney, which had to be removed in over 50 container transports. This was the second-highest tonnage ever removed from Lake Baldeney during a mowing season. Only in the particularly hot and dry summer of 2018 had the removal been even higher at over 700 tonnes.

Mowing is currently the only way to mitigate the restrictions on water sports. This was the result of the "Elodea II" research project, in the course of which other methods (subsoil cultivation with water pressure, harrowing or raking, competitive planting with low-growing armour algae) were tested without success.