The environmental organisation WWF is pleased with the decision, but it hopes that Russia would also join in the agreement.
The PSSA classification granted by IMO is recognition of the sensitivity and unique nature of the Baltic.
There has been a sharp rise in maritime traffic in the Baltic Sea, and the amount of oil transport is expected to increase considerably in the future.
Three other areas were given the same classification: the Canary Islands, the Galapagos Island, and the Torres Strait.