Fire officials are investigating what caused a boat to sink off the coast of Charles Island Monday.

Battalion Chief Jason Dombrowski of the Milford Fire Department says three people were transported to Milford Hospital, with one in critical condition as of Monday evening.

“We would like to thank the individuals on the oyster boat that actually did what they could to help these individuals that were in jeopardy,” Battalion Chief Dombrowski says. “Our hats go off to them for a job well done.”

The United States Coast Guard assisted in the rescue.

Officials say the other two people rescued are in stable condition, and the investigation is ongoing.