Why does the Stewardship Society not support the sinking of derelict ships in the Lakes as destinations for Scuba divers?

Artificial structures can form a good substrate for marine creatures both sessile and free-living to inhabit, in fact a number of concrete structures have been placed in the Lakes as habitat for lobsters by the Department of Fisheries and Oceans and the Eskasoni Fish and Wildlife Commission . However, sinking ships is another matter. A thorough cleaning to remove pollutants is necessary and very expensive if done properly. Even then, it is impossible to remove all noxious materials from pipes and inacessible corners of bilges. In the open ocean, tides and currents will remove and quickly dilute these residual toxic materials with little consequence. However, the Bras d'Or Lakes would be particularly vulnerable as there is very low flushing of waters. For instance, a complete exchange of water within Whycocomagh Bay would take well over two years, and St. Andrews Channel, about 1 year. The fastest flushing rates would be near the entrance to the Lakes in the Great Bras d'Or Channel where it would be less than a week.
Many marine biologists and oceanographers have raised concerns with this practice and Japan and California have banned sinking of ships for artificial reefs.