Sweden has an interesting history with its period of being a great power between 1611-1721 where a number of vessels foundered at sea. There are between 9,000 and 10,000 registered and documented shipwrecks of both wooden and steel vessel types.
There was a strong maritime tradition with thousands of vessels that were lost along the Swedish coastline. Researchers estimate that there are a total of 40,000 known wreck positions in the Baltic Sea. Sweden is in the unique position of not having any woodworm to destroy the wrecks as well as low-salt levels and preservation qualities of the water in the Baltic Sea.
Even the Swedish Tourist organization has recognized this and incorporated info about wreck diving in the country.
The Baltic Sea offers unique diving conditions hard to match anywhere in the world. The salinity is very low as well as the oxygen level helping to preserve the wrecks in pristine condition. Even wood details remain intact. You can often see furniture in cabins and other details.
To read more about wreck diving in Sweden also have a look at Ocean Discovery webiste. They are closely associated to the famous and highly respected organization Global Underwater Explorers.
Their website: http://www.ocean-discovery.org