The first Baltic Sea bathing areas have already been closed because of cyanobacterial blooms, even before the peak holiday season begins. Scientists have warned for years that rising Baltic Sea temperatures and persistent eutrophication are creating increasingly favourable conditions for such blooms. According to HELCOM, 94% of the Baltic Sea’s surface area is affected by eutrophication.
“Cyanobacteria are bacteria that develop as a result of excessive nutrient enrichment in water. Nutrients flow into the Baltic Sea, which may sound positive in itself, but their quantities are far too high. In this way, they feed cyanobacteria, which develop particularly intensively when water temperatures are high,” Marcin Kotlarek, President of the Race for the Baltic Foundation, told Newseria.
Excess nutrients feed cyanobacteria
Eutrophication is the process by which water becomes excessively enriched with nitrogen and phosphorus compounds. These substances reach the Baltic Sea mainly through municipal wastewater and agricultural runoff.
In the marine environment, they act like fertiliser for algae and cyanobacteria. Their excessive growth reduces the amount of light reaching deeper layers of water, while the decomposition of dead organisms can lead to the formation of so-called dead zones, where oxygen levels become dangerously low.
The Baltic Sea is particularly vulnerable to this process. It is a semi-enclosed sea, and a full exchange of its waters with the North Sea takes around 30 years. It is also relatively shallow, with an average depth of only about 52 metres.
Around 250 rivers flow into the Baltic Sea, while nearly 90 million people live in its drainage basin. As a result, pollutants accumulate over many years, and improvements in the ecosystem take place very slowly.
According to HELCOM, seven of the world’s ten largest marine dead zones are located in the Baltic Sea.
Warmer summers increase the risk of blooms
“Cyanobacteria increasingly affect the use of bathing areas because we are experiencing hotter summers more often. The Baltic is the second-fastest-warming sea in the world, behind only the Black Sea, which encourages cyanobacterial blooms,” Kotlarek explained.
The Baltic Sea is among the bodies of water most strongly affected by climate change. According to the Klimada 2.0 project, the temperature increase in its drainage basin is faster than the global average.
At the same time, the average temperature of Baltic waters has risen by around 1.5°C over the past 30 years. This is roughly three times faster than the average warming rate of the world’s oceans, creating increasingly favourable conditions for cyanobacteria.
“We can expect cyanobacterial blooms to become more frequent. On the one hand, this results from rising air temperatures, which also increase water temperatures. Another important factor is the pollution reaching the Baltic Sea. For decades, thousands of tonnes of phosphorus and nitrogen from wastewater and agriculture have flowed into the sea,” said Kotlarek.
“The Baltic is increasingly saturated with these nutrients, which feed cyanobacteria. The combination of higher temperatures and elevated concentrations of phosphorus and nitrogen means that blooms are becoming more common.”
Recovery will take years
Experts stress that improving the condition of the Baltic Sea will require time. Because it is semi-enclosed, the effects of pollution persist much longer than in most other marine areas.
Nitrogen and phosphorus compounds accumulated over decades remain in the ecosystem. Even after nutrient inflows are reduced, their environmental effects may continue to be felt for many years.
A cyanobacterial bloom does not always mean that toxins are present. However, it is impossible to determine whether water is safe simply by looking at its colour or surface appearance.
For this reason, sanitary authorities advise people not to enter water that has changed colour or contains visible cyanobacterial scum.
“Cyanobacteria are harmful to the body. Contact with water affected by a cyanobacterial bloom should therefore be avoided. This applies to both people and animals,” Kotlarek said.
The problem often begins far from the coast
According to the Race for the Baltic Foundation, the sources of the problem are often located hundreds of kilometres away from the coastline.
Reducing eutrophication requires further cuts in the amount of nitrogen and phosphorus entering the Baltic Sea. This includes investments in wastewater treatment, reducing nutrient runoff from agricultural land and limiting pollution entering rivers.
The issue is also highlighted by the “Do You See Cyanobacteria?” campaign, run by the Race for the Baltic Foundation as part of the “The Baltic Begins on Land” project.
