A large leak of an unknown substance occurred in the Gulf of Bothnia in the Baltic Sea between Sweden and Finland, Swedish Coast Guard reported.

It is still not clear what kind of substance got into the sea. The pollution covers the sea surface in the economic zones of Sweden and Finland and is located about 10 miles from the Swedish coast. The spill area is about 77 sq. Km, the statement said. The Finnish side has already been informed about the incident.

The spot can be compared in area with the city of Malmö (the third largest city in Sweden), the Swedish newspaper Aftonbladet comments on the incident.

The Swedish Coast Guard took samples from the spill in Swedish waters. Only after analyzing the samples, it will be possible to plan possible control and mitigation measures, the report says.