Earlier this week, Finnish media began reporting about a mysterious white substance washing up in clumps on the shoreline of Hanko, the southernmost point in mainland Finland.
The exact composition of the white substance remains unclear, but is thought to be some sort of vegetable-based oil mixture.
On Thursday, renewable fuel producer Neste said the white substance is likely to have come from the wash water of a vessel transporting cargo for the fuel firm.
The company said it accepts responsibility for the incident and will provide compensation for any damage it may have caused. It plans to review its operating instructions to ensure that similar incidents do not happen again.
The mixture has contained used frying fat, animal fat and vegetable oils. According to Neste, these fats are not dangerous to humans or the environment as such, but they certainly do not belong in nature, the company said in a press release.
A couple of days after the white substance began appearing, locals started noticing that dead fish were washing up on the shore.
However, the two incidents do not appear to be related, according to Markus Sillanpää, a researcher at the Finnish Environment Institute (Syke).
"There isn't an obvious link between the white substance and the dead fish. There's no need for particular concern about the situation," he explained.
However, authorities are still looking into the matter. For example, the Finnish Food Authority is examining the fish found on the shore for possible diseases.
According to local rescue services, the types of fish in question are mainly brisling sardines, also known as European sprat.
Although local residents may have been relieved to learn that the unknown white substance was probably vegetable oil, the material is not entirely harmless to the environment.
Tank washing
According to the US Environmental Protection Agency (EPA), vegetable oils can stick to things like birds' feathers and beaches like petroleum-based oil. Vegetable oils can also form toxic compounds and can be difficult to remove from environments once they have appeared.
According to the John Nurminen Foundation, a maritime environment protection group, releasing any sort of hardening substances into the Baltic is explicitly prohibited.
"[Boat] oil tanks should be cleaned in ports and the washing water should be left ashore," said Juulia Suikula, the foundation's project manager.
"However, international maritime traffic regulations are vague and difficult to monitor," she noted.
The foundation and the Finnish Transport and Communications Agency (Traficom) recently published a risk assessment of chemicals handled at the country's ports. Examples of substances that are still permitted to be discharged with washing water into the Baltic Sea include benzene, styrene and phenol.
"For example, Finland's pine oil industry operators are compelled to leave their waste washing water on land, and this water can be used for other industrial purposes. The Baltic Sea is vulnerable and deserves better, the current situation cannot continue," Suikula said.
4.10 pm: Added Neste information on source of the substance.
6.22 pm: Added Neste statement about responsibility and compensation, corrected spelling of Sillanpää's name.