The Baltic Sea is among the bodies of water most severely affected by eutrophication, a process caused by excessive levels of phosphorus and nitrogen. Although the inflow of these nutrients has declined significantly in recent decades, the condition of the ecosystem remains poor. Further improvement will require additional reductions in pollution, particularly from agriculture and wastewater.
“In very simple terms, eutrophication means excessive enrichment with substances such as phosphorus and nitrogen, scientifically referred to as nutrients. These substances are necessary for vegetation and plant growth, which is why they are used as fertilisers on fields. When it rains, they are washed into rivers and eventually reach the Baltic Sea through the river system,” Marcin Kotlarek, President of the Race for the Baltic Foundation, told the Newseria news agency.
Another major source of nitrogen and phosphorus pollution is wastewater, particularly leakage from poorly maintained septic tanks. This effectively provides algae and cyanobacteria with additional “fertiliser”, accelerating their growth.
“When algae and cyanobacteria bloom, they eventually sink to the seabed and decompose. This process consumes oxygen. As a result, oxygen-depleted areas develop, meaning that where this material accumulates, life can no longer survive. This is how dead zones are created,” Kotlarek explained.
An estimated 94% of the Baltic Sea is affected by eutrophication. Seven of the world’s 10 largest marine dead zones are located in the Baltic, accounting for almost 20% of its total area.
“If we look at maps from the 1960s, only around 10,000 square kilometres were affected by eutrophication and dead zones. Today, according to maps from last year, the figure is already 70,000 square kilometres. That is almost twice the area of Denmark,” the Race for the Baltic president said.
The Baltic Sea is particularly vulnerable
The Baltic Sea is characterised by a mixture of saltwater and freshwater. Its relatively low salinity is the result of substantial freshwater inflows from around 250 rivers, including eight major ones, combined with very limited exchange of saltwater with the North Sea.
A complete renewal of the Baltic Sea’s water takes around 30 years.
Its vulnerability is also linked to its relatively shallow waters. The average depth of the Baltic is approximately 52 metres. By comparison, the Mediterranean Sea has an average depth of around 1,450 metres.
“Scientists have calculated the maximum amount of pollution that can naturally enter the Baltic while still allowing the ecosystem to recover. Unfortunately, climate change, rising air temperatures and warmer seawater mean that this threshold is constantly shifting. The maximum permissible level calculated under a cooler climate is already too high. We are therefore in a race against time and against climate change,” Kotlarek said.
Poland has reduced nutrient pollution, but more needs to be done
According to a HELCOM report, between 1995 and 2022 Poland reduced total nitrogen inputs into individual Baltic Sea sub-basins by between 9% and 32%.
Poland has achieved the required nitrogen input limits for all sub-basins except the Baltic Proper, where a further 19% reduction is still needed.
In the case of phosphorus, Poland reduced its input into the Baltic Proper by 28%, but the amount entering the basin remains substantially above the agreed threshold.
Across the Baltic Sea as a whole, normalised total nitrogen inputs declined by 11% between 1995 and 2022, while phosphorus inputs fell by 32%.
“We can imagine the Baltic Sea as a bathtub into which heavily polluted water was flowing for decades. Even if we manage to reduce the amount of pollution entering it today, the ecosystem’s response takes much longer,” the expert explained.
Pollution from across Poland eventually reaches the Baltic
Eutrophication is not limited to the Baltic Sea. It is also a major problem affecting Polish rivers and lakes. More than three-quarters of them are considered eutrophic, containing excessive quantities of phosphorus and nitrogen.
“About 80% of the water entering the Baltic from Poland comes through the Oder and Vistula rivers, with the remaining 20% coming from smaller coastal rivers such as the Łeba and Parsęta. At the same time, 98% of Poland’s territory lies within the Baltic Sea drainage basin,” Kotlarek said.
This means that agricultural pollution originating hundreds of kilometres from the coast can ultimately reach the sea.
“Natural fertilisers leaking into soil and water in Wielkopolska eventually reach the Warta, then the Oder and finally the Baltic Sea. Likewise, wastewater leaking from a septic tank in the Podlaskie region can enter a river system that ultimately feeds into the Vistula and then the Baltic,” he explained.
The scale of the drainage basin shows why preventing marine eutrophication requires action on land, often far away from the coastline.
“The Baltic begins on land”
The Race for the Baltic Foundation wants to promote this approach through its “The Baltic Begins on Land” initiative. The first part of the project is a nationwide educational campaign entitled “Do You See Cyanobacteria?”
“People often visit the seaside once a year, spend a week or two there and encounter a cyanobacteria bloom. They become angry with the local tourism industry, municipalities or hotels. But in reality, those of us arriving from central, southern or any other part of Poland also contribute every day to the conditions that lead to beach closures,” Kotlarek said.
“What we do throughout Poland, almost all of which lies within the Baltic drainage basin, affects what eventually reaches the sea through rivers. It is important that everyone understands the connection between what happens in the sea and what we do in our everyday lives, including the way wastewater and natural fertilisers are managed by households and businesses.”
Foundation aims to cut phosphorus inflow by 500 tonnes by 2030
The Race for the Baltic Foundation has set a target of reducing phosphorus inflows into the Baltic Sea by 500 tonnes by 2030.
Its work focuses primarily on agriculture, wastewater management and ports.
“We are working, first of all, to reduce pollution from agriculture, wastewater and ports, where fertilisers, grain and other bulk goods are handled. If these materials are not properly secured during transshipment, they can contribute to algae and cyanobacteria blooms,” Kotlarek said.
The foundation sees potential for cooperation with farmers, local authorities, ports and manufacturing companies.
“This is a long-term process because the simplest solutions, such as investments in large wastewater treatment plants, have largely already been implemented. What remains requires more targeted action with farmers, municipalities, ports and businesses,” he added.
The challenge is therefore increasingly about preventing diffuse pollution rather than relying solely on large infrastructure projects. With climate change making the Baltic Sea even more vulnerable, reducing nutrient inputs from across its vast drainage basin is becoming an increasingly urgent task.
