A St. Mary's County man reported missing from the fishing pier at Point Lookout State Park on Thursday afternoon may be lost in the Chesapeake Bay, authorities said Friday.

About 2 p.m. Thursday, Lewis E. Blackistone, 29, left his fishing partner on the pier and went back to shore to get more bait or a crab trap, according to accounts from the Maryland Natural Resources Police and the U.S. Coast Guard.

At 5:15 p.m., Blackistone still had not returned, so his friend reported him missing to a park employee.

Helicopters and boats from the Natural Resources Police and the Coast Guard, as well as local fire and rescue department dive teams, searched for Blackistone without success.

At 2 p.m. Friday, the operation was downgraded from rescue to recovery, and the Coast Guard withdrew.

But Cpl. Ken Turner, spokesman for the Natural Resources Police, said it is possible Blackistone is on land.

"We are treating this as a missing person case. We're checking out the water, and we're checking out the land," Turner said. "Just because we went from search and rescue to search and recovery, we're not saying that this individual is in the water."

The Coast Guard called in helicopters from as far away as Atlantic City, N.J., and Elizabeth City, N.C., to help in the search.

Blackistone, 4 feet 11 inches tall and 145 pounds, is "a swimmer, but not a strong swimmer," said Scott Winslow, a Department of Homeland Security civilian search and rescue specialist who was serving as a duty officer for the Coast Guard station in Baltimore.

Authorities found Blackistone's shoes on the shoreline, with his socks neatly tucked inside. They also found an identification card and a credit card in one of his shoes. Alongside the shoes were a pair of sunglasses and some loose change.

A camper told the authorities that he heard a cry for help coming from near the pier about 2 p.m. Thursday, but Turner said it was impossible to confirm that the cry came from Blackistone or whether it occurred at all.

Blackistone frequently fished at the park, said Diana Riley, who has lived at Point Lookout State Park for 16 years. Riley, who said she had not seen him there recently, said he rode a bicycle or walked to the park.

The Natural Resources Police said Friday that they will continue to search for Blackistone.

Staff researcher Bobbye Pratt contributed to this report.