A close look at recreational boating on German lakes

Researchers from the University of Konstanz’s Limnological Institute and the Brandenburg State Office for the Environment closely studied the effects of growing motorboat usage on lakes and developed recommendations to make boating more environmentally friendly. In the research project SuBoLakes (Sustainable Boating on Lakes in Germany), which was conducted between 2021 and 2025, the team investigated the impact of boating on several lake districts in Germany. The results of this project have now been published in a detailed report.

In contrast to the global goals of the European Water Framework Directive (WFD) that should be met by 2027, most of Germany’s lakes are not in a good ecological state. This is due to a broad array of anthropogenic interferences. One of these is motorized water sports, which has a negative impact on the vulnerable lakeshore zone, for example, as a result of wave action, waterside constructions and spaces used for boating infrastructure such as docks and marinas.

Ship waves damage shorelines

“Passenger ships and big motorboats negatively impact shorelines near their routes. The waves generated by these vessels affect the plants and animals living in the shallow water zone and can resuspend and displace sediments,” explains Frank Peeters, professor of environmental physics at the University of Konstanz.

Peeters, who coordinated the SuBoLakes project, measured ship waves and modeled their spread across the lake. He found that the impact of ship waves at the shoreline depends on the number of ship passages in front of a shoreline location and on the height and length of the waves generated by the vessel.

Smaller ships produced smaller waves than larger ones. And the slower a ship moves, the smaller the height and wavelength of the ship wave. In addition to this, waves decrease in height the farther they travel.

As a result, Peeters recommends limiting the intensity of boat travel and the maximum size of recreational boats, setting minimum distances from the shore for ships traveling parallel to the shoreline and defining corresponding speed limits.

“In highly vulnerable areas there should be regulations for more distant navigation routes and speed limits,” Peeters suggests. “For such measures to be effective, ships must reduce their speed significantly some time before they enter these areas.”

Particularly harmful at low water levels

The shallow water zone which is impacted by ship waves also depends on the lake level. With this in mind, the researchers warn against expanding recreational and passenger ship travel in periods when water levels are low, for example, during the winter season on Lake Constance. Instead, they argue that more frequent low water periods must be addressed with an adaptive strategy within new concepts for sustainable recreational boating.

Yet, even when leisure boats and passenger ships lie still in the harbors, they will cause environmental problems. Not only do they release pollutants into the water, e.g., biocides from conventional anti-fouling paints, but the main issue is that berthing infrastructure encroaches on valuable aquatic ecosystems.

There is a very high density of boats on Lake Constance—112 watercraft per km² of lake surface or about one boat per 5 m of shoreline. By comparison with the total number of boats in both Germany and Switzerland, the lake holds about 10% of the amount of boats in both countries.

On Lake Constance alone, approximately 618 individual buoy fields, docks, harbors, marinas and other kinds of berthing facilities cover an area of more than 4.4 km². Each officially authorized berth requires an area of 150 square meters on land and on the water.

A new method based on aerial images developed by researchers at the Limnological Institute reveals the spatial extent and ecological impact of berth infrastructure. “We see a lot of negative effects on the aquatic environment that, in light of increasing water tourism, we simply cannot ignore,” says Wolfgang Ostendorp from the Limnological Institute.

He would like to make the analytical procedure available to the relevant authorities and motorboat sport associations, as a decision-making tool to help them exercise more restraint when it comes to valuable shoreline ecosystems.

An appeal to policy makers

“Overall, we currently have an insufficient data and planning basis in the area of motorized water sports,” emphasizes Ralf Köhler from the Brandenburg State Office for the Environment. “This means we cannot ensure that the future development of the recreational boating and passenger ship sector is compatible with the goals of environment and nature conservation.”

The authors of the study fear that an intensification of passenger transport and recreational boating on lakes in Germany (water tourism) will significantly increase the negative impacts on shoreline ecosystems if no protective measures are taken.

“Local action is necessary in order to respond to acute problems and provide optimal protection for littoral areas that are at high risk. In addition to this, Germany needs a nationwide strategy for developing sustainable motorboat sport activity on its lakes that ensures water and nature conservation are given appropriate consideration,” says Köhler.

The report is not just aimed at authorities. “Of course, skippers, regional planners and the tourism industry should also be included in the decision-making process,” project leader Peeters says.