Päivi Haapasaari: The shadow fleet heightens the environmental risks in the Baltic Sea

The environmental risks associated with maritime traffic in the Baltic Sea have long been recognized, and the current geopolitical situation has only intensified these concerns. The Baltic Sea is one of the world’s busiest sea areas, with the primary concern being cargo ships transporting liquid products such as crude oil, oil products, and chemicals from Russia. Additionally, since all large ships carry substantial amounts of fuel, any shipping accident carries the risk of an oil spill.

The ongoing Russian war in Ukraine and the subsequent sanctions imposed by Western countries have led to a shift in trade patterns. European nations have reduced their reliance on Russian oil while countries in Asia and Africa have emerged as new trading partners for Russia. This shift has resulted in a transition from legally registered commercial tankers to a shadow fleet with unclear ownership and frequently changing flag states.

This fleet poses a significant hazard to the Baltic marine environment, as evidenced by numerous incidents that have occurred globally including, for example, in the Danish Straits. The shadow tankers are often outdated, in poor condition, and prone to technical defects, with inadequate insurance coverage. Many of these vessels operate without the double hulls required by international regulations and may also neglect ballast water management which is essential for preventing the spread of invasive aquatic species and harmful pathogens. It is known that some shadow tankers have falsified their location data or deactivated their AIS systems to conceal their operations in Russia. Additionally, these vessels have been linked to the sabotage of underwater infrastructure, potentially damaging the seabed. It is also suggested that these tankers have previously conducted hazardous ship-to-ship cargo transfers at sea. Moreover, Russia’s interference with the navigation system (GNSS) to protect its oil terminals and refineries from drone attacks has led to ships deviating from their courses, putting them at risk of running aground. This disturbance is believed to have led to four near-miss incidents in the Gulf of Finland during autumn 2024.

Risks of navigation
The Baltic Sea presents a particularly challenging environment for navigation. The sea is shallow with narrow waterways, and its archipelagos require ships to navigate around rocks and skerries, increasing the risk of groundings. The waterways intersect east-west and north-south, raising the likelihood of collisions. During the winter and autumn months, ice conditions and limited daylight hours make navigation even more perilous, particularly for crews unfamiliar with the region’s conditions. A lack of safety culture onboard exacerbates these risks.

Environmental impacts of accidents   
The Baltic Sea is a unique ecosystem characterized by brackish water, shallow depths, limited water exchange, and diverse habitats that support a variety of distinctive marine and freshwater species, including endemic ones. It is home to several threatened species and serves as an important migratory area for arctic birds. These characteristics make the Baltic Sea ecosystem particularly sensitive to environmental disturbances, and highly vulnerable to the effects of oil and other harmful substances, which can accumulate in the food web. The slow circulation of water allows pollutants to persist for extended periods, which further amplifies their impact.

Assessing the environmental impacts of maritime accidents is challenging, yet essential for effective recovery planning. The consequences depend on factors such as the location, season, and timing of the accident as well as the properties and behavior of the substance leaking into the sea. Interactions between harmful substances and the ecosystem are complex, and real-time tracking of spills can be difficult. The long-term and cumulative effects may only become apparent over time. While the effects of oil spills are somewhat understood, chemical pollutants encompass a wide range of substances, each with unique behaviors that may be even more difficult to manage and recover than oil. Tankers can carry multiple types of chemicals simultaneously, meaning an accident could involve a mixture of substances spilling into the sea.

Certain areas, habitats, and species are more vulnerable to contamination than others. For example, seashore meadows and sandy beaches are considered the highest-risk areas for oil spills due to their slow and uncertain recovery, and the difficulty of cleaning them. The most severe acute impacts of an oil spill are typically experienced by seabirds, whose mortality rates are highest and recovery often the most challenging. In addition to birds, some crustaceans, aquatic plants, and littoral fish, as well as seals are among the most sensitive species to the long-term impacts of oil.  

Managing risks
The outdated tanker fleet, along with other unforeseen hazards arising from the current geopolitical tensions, has heightened the need to strengthen risk management and preparedness for adverse events. Sharing information among states and authorities to understand both safety and security risks, and agreeing on measures to control or restrict the use of the shadow fleet is crucial for preventing accidents.

The Baltic Sea countries have a robust system of national and regional cooperation for responding to oil and chemical accidents, with established protocols, joint response mechanisms, and regular training exercises. However, response actions vary depending on the substance involved and the specific conditions, making each case unique.  

Science plays a key role in advancing the understanding and management of risks. Two new research projects – CoWup [1] and WATERWAYS [2]  – focusing on marine and maritime risks in the Baltic Sea began in January 2025, funded by the Strategic Research Council of Finland. Involving a wide range of expert stakeholders, these projects aim to identify and analyze environmental, operational, security, and geopolitical risks, with the goal of enhancing society’s ability to monitor, prepare for, and respond to undesirable events.


[1] Coastal waters under pressure – safeguarding a healthy Gulf of Finland in a changing geopolitical and environmental landscape.
[2] Marine waterways as a sustainable source of wellbeing, security, and safety.