Lake Constance is far more than just one of Europe's largest inland waterways: it is a sensitive ecosystem and supplies millions of people with drinking water. But the lake is changing. A lack of deep mixing, extreme water levels and invasive species such as the quagga mussel are putting the water under stress. Skippers can make a contribution to preserving the area: opt for electric drives or synthetic fuels, use biocide-free antifouling and treat nature conservation rules with respect.
This is why winter circulation fails to materialise
Until a few years ago, the oxygen-rich surface water cooled in winter, became heavier and sank to a depth of 251 metres. Nutrient-rich deep water was displaced and rose to the surface. This cycle supplied organisms at the bottom of the lake with oxygen and brought nutrients to the surface for the growth of beneficial diatoms: the basis of the food chain in the Lake Constance ecosystem. For eight years now, the winters have not been cold enough for this process. While important nutrients are missing at the surface, the increasingly warm, stagnant water favours the spread of less desirable species such as blue-green algae. The ecosystem is shifting: specialised species are gradually disappearing, while warmth-loving generalists are spreading.
The oxygen supply has not yet collapsed. At the deepest point, in the Obersee part of Lake Constance, around six to seven milligrams of oxygen per litre were measured this winter, and significantly more at the surface. Oxygen is therefore reaching the bottom, but no longer at the level that would be ideal for a robust system. In shallower lake regions such as the Bregenz Bay and Lake Überlingen, circulation is still functioning.
More extreme water levels - but no ecosystem damage in the lake so far
The water level of Lake Constance fluctuates by around 1.2 metres every year, depending on the amount of rain and snow. Climate change is exacerbating these fluctuations. Other relevant influencing factors are alpine hydropower with its reservoirs, historical construction measures at the outlet of the Obersee and plant growth in the Seerhein. The reason for the fluctuating water level over the course of the year is the varying amounts of water that enter Lake Constance. The amount of water flowing out of the lake, on the other hand, changes less because Lake Constance is one of the few unregulated Alpine lakes.
More on the fluctuating water level at Lake Constance:
According to Dr Gernot Längle, Chairman of the IGKB, the low winter water levels have so far had no negative impact on the lake's ecosystem. The usual annual cycle with water levels over one metre higher in summer is maintained. For the sensitive shallow water zone and the reed beds, however, timing is important. If the water rises too late in spring or recedes considerably in winter, fish lose their spawning grounds and water birds lose their protected breeding grounds.
Especially in the winter and spring months, skippers should check the current weather conditions before every trip. Water level check. Avoiding shallow bays at low tide not only protects your keel from grounding, but also spares the stressed retreats of the shore fauna.
Invasive quagga mussel as a stowaway
Introduced from the Black Sea region, the quagga mussel now colonises the lake bed of Lake Constance in densities of sometimes 800 to over 10,000 specimens per square metre. It filters large quantities of water and extracts food for plankton, which in turn is an important food source for fish. It also colonises pipes and buoys and clogs waterworks pipes.
For skippers, the quagga mussel is more than just an ecological nuisance: it attaches itself to hulls, increases frictional resistance and, in the worst case, can clog cooling water pipes. Anyone trailering their boat into other waters must be particularly careful.
Important for cleaning: Simply spraying with a garden hose is often not enough. The microscopic larvae of the mussel are very resistant. Experts advise cleaning the boat and trailer professionally and hot when changing water. Only water temperatures of over 60°C ensure that the larvae are reliably killed. Particular attention should be paid to hard-to-reach areas such as the anchor locker, bilge water and the engine cooling circuit.
Transfer rules in Switzerland
Anyone planning to transfer their boat to Swiss waters should be aware of the strict rules of our neighbours: In many cantons, there is now a strict cleaning obligation for boats that were previously moored in another body of water (such as Lake Constance).
- Certificate: Skippers often have to provide proof of professional cleaning by means of a registration confirmation or certificate. Special online portals have been set up for this purpose, which are used to register a planned change of water. Following cleaning at an authorised cleaning centre, a water entry permit is issued.
- Controls: Without the in-water authorisation as proof, launching may be refused. Find out in advance from the relevant shipping authorities (e.g. Canton Thurgau or St. Gallen) to avoid fines and a compulsory stop ashore.
Electromobility, HVO diesel and biocide-free antifouling
Sonja Meichle shows that environmental protection and water sports are not a contradiction in terms. As head of the largest marina on the lake and Vice President of the German Water Sports Industry Association, she combines a passion for water sports with ecological responsibility. Her credo: the industry is not waiting for bans, it is already providing solutions.
Lake Constance is becoming a pioneer for clean drives. Meichle explains that the trend for small outboard and inboard engines has been moving towards electric drives for years. Technical developments such as bipolar charging and range extenders are still pending for larger engines, but a lot is currently happening in this regard. The charging infrastructure in the harbours around the lake is being massively expanded at the same time to make the transition a success.
For all those who are still travelling with combustion engines, there is an uncomplicated solution that has an immediate effect. Meichle confirmed this to the Yacht editorial team:
"All three German marine petrol stations have already switched to synthetic HVO diesel."
As she has already emphasised in previous reports, conventional diesel engines can use this fuel without any problems or residues. HVO is certified to EN 15940 and approved for most modern diesel engines without conversion. Until electromobility is technically mature for larger engines, CO2 emissions can be massively reduced immediately. A side effect that will please the crew: The annoying diesel odour in the cockpit will also be a thing of the past.
A rethink is also taking place when it comes to antifouling. What was still viewed with scepticism last year is now becoming the standard, according to Meichle: "Experience to date with biocide-free antifouling is good. It works - depending on factors such as water temperature and how often the boat is used, of course." In her marina, the recommendation is clearly in favour of biocide-free products.
Personal responsibility instead of paragraphs
While many cantons in Switzerland rely on strict registration procedures and mandatory cleaning against the quagga mussel, Meichle relies on personal responsibility and knowledge. Rigid rules are difficult to control, especially with SUPs or small boats.
Sonja Meichle is convinced:
It's better to focus on education and awareness-raising so that people voluntarily behave prudently. You won't get very far by imposing rules."
Your marina will therefore become a place of learning: Skippers will learn everything about environmentally friendly care, saving drinking water and the correct hot cleaning when changing waters. The goal is clear: to preserve Lake Constance as an ecosystem and a sailing area, with understanding instead of regulations.
Checklist for skippers: How to protect Lake Constance
- Conserve resources: Clean the deck with seawater instead of precious drinking water and only use biodegradable cleaning agents.
- Professional hot cleaning for water changesKill quagga mussel larvae by cleaning at over 60°C when changing water.
- Immersion authorisation for transfer to SwitzerlandMake sure that you have a launching licence before you trailer your boat in Swiss waters.
- Environmentally friendly coatings: Use biocide-free antifouling to protect the water quality.
- Refuel with HVO diesel: Refuel with renewable HVO diesel instead of fossil fuels to reduce your ecological footprint.
- proper disposal: Only dispose of your waste water and rubbish at the designated stations in the harbours.
- Respect riparian zones: Strictly adhere to the speed limit within the 300 metre zone (a maximum of 10 km/h is permitted). Stay away from reed beds voluntarily, even when sailing, so as not to disturb breeding birds
- responsible anchoring: Anchor only in the designated zones and observe the maximum mooring time of 24 hours.
- Avoid protected areas: Do not drive on marked nature reservesto preserve the local flora and fauna.
- Avoid keel contact: Do not enter shallow areas. Swirling up sediment damages aquatic plants and disturbs the ecological balance of the shallow water zone.
This might also interest you:
- After heavy rainfall on Lake Constance: Driftwood forces harbour closures
- Kressborn on Lake Constance: Following the tourist tax judgement, more and more municipalities want to extend the tax to boat owners
Antonia von Lamezan
Volontärin
