Updated, 7:52 p.m.
The Norwalk Fire Department boat is returning to shore, according to emergency dispatches.
Norwalk firefighters responded to a "mayday" call Saturday afternoon from a boat reportedly sinking off the coast of Sheffield Island, according to emergency dispatches.
Officials reportedly weren't able to locate the boat after their initial search and Marine police, fire units from multiple towns and the U.S. Coast Guard are now aiding in the search.
The call came in at about 5:45 p.m.
Harold F. Cobin contributed this report.