PORTLAND (AP) — The Coast Guard has suspended its search for a boat that sent a distress signal Saturday afternoon in Maine.

Authorities say the mayday call came in around 4:40 p.m. Saturday from an unknown source. Radio equipment indicated it was made from Casco Bay, about one mile east of Jewell Island. The Coast Guard sent out a helicopter, plane and three boats but didn’t find anything.

The search was suspended Sunday afternoon after crews searched more than 520 square nautical miles.