Brandenburg’s Scharmützelsee is located just 50 minutes outside of Berlin and is a popular recreational destination, especially in summer. But, since July 2025, visitors have been sharing the lake with a permanent yellow guest: a 200-kilogram buoy. It uses satellite data to monitor water quality and algae growth as part of the “Algae Monitor” project (source in German only). The buoy determines the algae concentration in the lake as precisely as possible on a daily basis so that countermeasures can be taken at an early stage in the event of anomalies.
The algae monitoring buoy hits Scharmützelsee. Importance and potential of algae
Algae, whilst overlooked as pond scum by most, are a vital part of our planet’s ecosystem. It plays a crucial role in everything from the air we breathe to the food we eat. They’re tiny powerhouses that absorb massive amounts of carbon from the atmosphere and produce a significant portion of our oxygen.
These aquatic wonders also form the foundation of the marine food chain, providing essential nutrients for countless organisms. In fact, the omega-3 fatty acids you get from fish originally come from algae. Beyond that, algae are packed with proteins, fibre, iron and vitamins.
You likely consume algae products daily without even knowing it! Ingredients like alginate, agar-agar and carrageenan—all derived from processed algae—are used to add firmness and stability to common products like candies and toothpaste.
However, the potential of algae is far from fully understood. According to the EU Commission, algae is a “sustainable means of producing an almost infinite variety of valuable products”, including food, pharmaceuticals, plastics, fertilisers and biofuels. The Bremen-based company Phytolutions, for example, relies on algae as an alternative to paraffin and is convinced that aeroplanes could be powered by “algae fuel” in the future. RESET has also already reported on the diverse application and processing possibilities of algae, in addition to biofuel production, for example, their use in clothing, 3D printing, the construction industry—even flip flops.
Overview of the functions of algae
Source of oxygen: Around 50 percent of the world’s oxygen is produced through algae photosynthesis.
Carbon sink: Algae absorb vast amounts of CO₂, acting as a natural brake on greenhouse gases.
Foundation of the food chain: They are the primary food source for many marine animals.
Versatile applications: Algae are used as thickening and stabilizing agents in food, cosmetics, and pharmaceuticals.
Sustainable resource: Algae grow rapidly without the need for arable land. Many species thrive in the sea and require no freshwater, while freshwater algae use significantly less water than land-based crops.
Source of oxygen: Around 50 percent of the world’s oxygen is produced through algae photosynthesis.
Carbon sink: Algae absorb vast amounts of CO₂, acting as a natural brake on greenhouse gases.
Foundation of the food chain: They are the primary food source for many marine animals.
Versatile applications: Algae are used as thickening and stabilizing agents in food, cosmetics, and pharmaceuticals.
Sustainable resource: Algae grow rapidly without the need for arable land. Many species thrive in the sea and require no freshwater, while freshwater algae use significantly less water than land-based crops.
When algae gets risky
Under certain conditions, however, algae can proliferate too much and become a health risk for humans and animals. “More sunlight, higher temperatures and heavier rainfall allow this species to spread in a way that is not very favourable. Climate change is now contributing to the rapid proliferation of algae and their growth in places where they did not previously exist,” says Fabrice Pernet, researcher at the Institute of Marine Biology, Ifremer.
While rising water temperatures play a role, the main culprit is often eutrophication, or the over-fertilisation of water bodies. This happens when there are excessive amounts of nutrients like nitrates and phosphates from things like wastewater and agricultural fertilisers. Normally, these substances are harmless in small doses. But, too much of a good thing can throw the entire aquatic ecosystem out of balance.
The result is explosive, uncontrolled algae growth, which can lead to the release of dangerous toxins.
A tragic example of this occurred in August 2022 in the River Oder. Here, a high salt content in the water fueled a massive bloom of the brackish water algae, Prymnesium parvum. This particular algae releases toxins that are lethal to fish and other aquatic life. According to the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), this environmental disaster resulted in the death of an estimated 1,000 tons of fish.
A current example of the consequences of the “algae plague” is Brittany. Here, green algae are currently proliferating on a massive scale and threatening oyster farming. And in Lower Saxony, blue-green algae is currently spreading, which is why bathing bans and warnings have been issued at many lakes.
Holistic monitoring using satellite data, measuring buoys and AI
Since the disaster in the River Oder, there have been nationwide calls for better monitoring of algae growth in water bodies and rivers. As the growth processes of algae often take place quickly and over large areas, traditional monitoring strategies are not sufficient in many places. This is why there is an increasing focus on digitally supported remote sensing of water bodies using real-time data.
The EU’s Copernicus programme provides the technical basis for monitoring algae growth in bodies of water and rivers. This programme, coordinated by the European Commission, collects huge amounts of data using satellite-based earth observation. Water remote sensing, in turn, relies on this data to identify areas with high algae concentrations.
Algae blooms stand out clearly in satellite images due to the concentration of the leaf pigment chlorophyll. Based on the colour indications provided by satellites, institutions such as the European Space Agency use algorithms and AI to calculate algae indicators to measure the chlorophyll content in the water and determine the algae concentration.
The nuts and bolts of algae monitoring
At some locations, including Lake Scharmützel, Lake Arendsee in Saxony-Anhalt and the Steinhuder Meer in Lower Saxony, this satellite data is supplemented by the use of local measuring buoys. This is the case with the “Algae Monitor”. The measuring buoy in Lake Scharmützel measures water temperature, conductivity, pH value, oxygen and algae quantity as well as meteorological data such as wind, air temperature and solar radiation. Oxygen and chlorophyll concentrations in the water are determined every 15 minutes. The combination of daily satellite and measurement data allows water quality and algae growth to be monitored continuously and comprehensively. Lake Scharmützel was chosen as one of the locations for a measuring buoy because a research station at the Brandenburg University of Technology Cottbus-Senftenberg (BTU) has been collecting data on the lake for 30 years. This data, together with current data, will be incorporated into the “Algae Monitor” project. The project is being initiated by the Federal Institute of Hydrology (BfG) in cooperation with the Helmholtz Centre for Environmental Research (UFZ) and the Federal Environment Agency.
The buoy for algae monitoring in use on the water. Water protection needs holistic climate protection
The measuring buoy in Lake Scharmützel, which took four years to construct, is to be used until 2027. The aim of the team led by Karsten Rinke from the UFZ is to learn from the continuous data collection and analysis, which chlorophyll values match which satellite images. The systems used are to be trained in such a way that this knowledge can be transferred to other bodies of water to assist in their protection.
Rinke is confident that the combination of satellites and local measurements will act as an effective early warning system for river and water protection. At the same time, however, Rinke warns of the significant effects of climate change.
“We have changed things in agriculture and we have improved our wastewater treatment. But many of the positive effects that we have achieved as a result are currently being cancelled out. Climate change means we are basically back to square one. The result will be that we will have to go much further down with the nutrient load than we always believed.”
The project at Lake Scharmützel demonstrates the potential of using technology to monitor ecological changes in real time. By combining satellite images, local buoy data and AI-powered analysis, scientists can now detect changes in ecosystems earlier than ever before. This allows them to take targeted actions to protect the water.
This type of smart monitoring is especially crucial as climate change poses new challenges for water protection. As Rinke emphasises, it’s essential to address these root causes of climate change. Only then will we be able to preserve our rivers and lakes for the long term.
