The main environmental problem of the Baltic Sea is that too many nutrients are being released to the sea (eutrophication). As many of the ‘easy’ measures to reduce the load from land-based sources have been put in place, increasing attention is given to measures to reduce the release of nutrients from the seabed sediments through the use of various technologies at sea, i.e. ‘sea-based’ measures. There is no specific legal framework available for sea-based measures, but a number of provisions set general obligations to protect and preserve the marine environment. The analysis indicates that neither the type of measure nor the geographical location of the activity is of decisive importance for the legal rights and obligations involved. Instead, the legality of any sea-based measure depends on the risks they present balanced against their benefits. There is considerable uncertainty on all these issues, and the matter is further complicated by the fact that both the risks and the benefits of the measures relate to their environmental impact. It is recommended that a regional risk-based framework is established for assessing when and how further research on sea-based technologies can be undertaken in the Baltic Sea.