Authorities said a gray whale lingering in San Diego Bay has yet to rejoin the annual migration from the lagoons of Baja California to Alaskan waters.

The U.S. Coast Guard sent a 33-foot boat, with a whale expert from the U.S. National Marine Fisheries Service on board, today to observe the roughly 30-foot whale, which has been in the bay since Tuesday, said Coast Guard Petty Officer 2nd Class Jetta Disco.

The expert will also check on the whale's condition and make sure it has not been struck by a boat, the USCG spokeswoman said.

The whale has been spotted in the Bay's broad channel, between the Star of India and Harbor Island, and has been surrounded by boaters during daytime hours. The swarm prompted a mid-afternoon Friday report of a vessel striking the sea mammal.

That report turned out to be false, according to the U.S. Coast Guard.

Coast Guard volunteers have been warning boaters to stay clear of the whale, as federal law forbids mariners from approaching leviathans, Disco said.

"We're just urging boaters to stay at least 100 yards away and give the whale plenty of room to maneuver and not get too close to it when they're out there," USCG Petty Officer Henry Dunphy said.

Experts are reluctant to try to herd the creature toward the ocean, fearing that would further stress the creature, which is believed to be about a year old.

According to Joe Cordero, a marine biologist with the Marine Fisheries Service, the whale probably ventured into the bay looking for something to eat.

Grays spend summers off Alaska, then travel south to the protected lagoons of Baja California, where their calves are born during winter months. The trip covers about 10,000 to 12,000 miles.

Usually around the end of February, the southbound stragglers mix with early migration whales heading north, so it's hard to say which way the whale in San Diego Bay was headed when he left the open ocean, Cordero said.