A hammerhead shark was spotted in the water at Ocean City, Maryland on Wednesday and Thursday, the Ocean City Beach Patrol confirmed to NBC Washington.
Many beachgoers have also seen the shark, according to social media reports.
Capt. Butch Arbin of the Ocean City Beach Patrol said the shark was likely sick or injured because they usually don't come that close to shore.
"We do believe it's sick or injured and because of that, its behavior is not normal..." said Arbin.
Late Thursday afternoon, the shark was seen being pushed by a current into the Assawoman Bay, away from Ocean City, Arbin said.
But before that, the shark apparently spent much of Thursday near the Ocean City shore. Beachgoers took photos and videos of the shark swimming through the waves and, in at least one case, coming right up to the shore.
Authorities spent much of Thursday warning people there was a hazard in the water, First Lt. Skip Lee of Ocean City Beach Patrol said.
"People are self-monitoring the situation and nobody is acting foolishly," Lee said earlier Thursday.
"I saw him or her at 6:30 this morning... I got to watch it come up and do its little thing and it went back into the water," he said.
Lauren Williams-Rowe posted an Instagram photo of the shark, which she snapped around 11:30 a.m. Thursday, she told NBC Washington.
"No swimmers today...thanks shark," she posted on Instagram.
Most species of hammerhead sharks "are fairly small" and are harmless to humans, according to National Geographic. Hammerheads typically weigh between 500 and 1,000 pounds and can grow to 13 to 20 feet long. The shark spotted at Ocean City is smaller than that, according to Lee.
He took his photo at low tide, showing the shark on the sandbar about 15 meters off shore.
"So you can see she's kind of looking away from us... with her head facing out toward the ocean..." Lee said. "You can see her back tail is very very long."
Hammerheads tend to migrate en masse in the summer, seeking cooler water, according to National Geographic.
However, Lee said this shark was behaving uncharacteristically by beaching itself on a sandbar. Authorities alerted the National Aquarium in Baltimore.
"Sharks live and swim in the ocean all day every day and we don't see them," he said. "So the fact that she beached herself on the sandbar, sharks don't typically do that."
Arbin said lifeguards were actively watching for the shark and would move people from the water periodically when they saw it come by.
"This morning as the shark came down the beach, the lifeguard would blow their whistles and get people out of the ocean to allow the shark to go by," he said.
Swimmers should never enter the water before 10 a.m. or after 5:30 p.m., when lifeguards are off-duty, Lee said.
Authorities will continue to monitor the situation in case the shark returns, the Beach Patrol said.
"We respect the ocean; she lives there and we're trying to give her her space," Lee said.
Arbin said has never been a shark attack in the history of Maryland.