The Baltic Sea is a unique sea in many ways. The good side of the sea is that there are hundreds of shipwrecks in the waves of the Baltic Sea. The wrecks are up to 1000 years old and their well-preserved. The Baltic Sea is the only sea that has this feature of preserving the wooden- and steel shipwrecks. This feature is caused by the small amount of oxygen, and the lack of shipworms.
The bad side of the sea is that it is the most polluted sea in the world. This complicates diving in the Baltic Sea. Luckily there are many projects for cleaning the sea, and hopefully in the future the sea will be cleaner.