Lifeguards and swimmers spotted the shark some 100 to 150 yards off Nauset Beach in Orleans Saturday afternoon. The 12-14 foot shark was last seen swimming away from shore.
No one was hurt, but some 3,000 swimmers at the beach were asked to get out of the water when the shark was sighted.
"Everyone was very relaxed and the shark put on quite a show moving back and forth out in front of the beach, but it was done in a very orderly fashion," Harbormaster Dawson Farber said.
A photograph shows the shark's dorsal fin behind a man in a kayak, but the man was able to reach dry land unhurt.
Farber said swimmers should "use some common sense, keep their eyes open, avoid swimming in close proximity to seals, and just to generally pay attention to their surroundings."
This sighting is not the first in the area this season. In early June, two great whites were detected off the coast of Cape Cod by acoustic receivers.
According to Greg Skomal, a senior biologist at the Massachusetts Division of Marine Fisheries, those two sharks had been tagged by the department just last year.
Skomal said the number of white sharks detected in New England waters has been increasing since 2008, because of the region's increased efforts to protect marine mammals.
"The elbow of the cape has these large, dense concentrations of gray seals now, and these white sharks go to the area to feed," he said. "Because the seals are so abundant, now the white sharks are paying more attention."
Skomal said the gray seal population off Cape Cod has grown from 10,000 to more than 300,000 since protections were put in place.
But Skomal said beach goers need not worry about impending shark attacks. The seals are located in a national wildlife refuge that is difficult for people to reach.
"Sharks are not there to feed on people; they're there to feed on seals."
However in Northern California on Saturday, an 18-foot great white bit through the front-end of a kayak near Pleasure Point, a popular surfing spot.
The kayaker, who was fishing, was thrown into the water but was unharmed and pulled out by a boater nearby.
Sean Van Sommeran of the Pelagic Shark Research Foundation inspected the kayak and confirmed the bite marks were those of a great white. He says it's unusual to see a shark attack a kayak.
"It's the first attack on a kayak that I know of for that stretch of the coast," said Van Sommeran.
Santa Cruz County Sheriff's Department Sgt. Esther Beckman said the man was in shock but otherwise unharmed, and recovering at home.
"He was very fortunate that in fact there were other boaters nearby who were able to rescue him and help him get out of the water," Beckman said.
ABC News Radio and Alexis Shaw contributed to this report.
- Nature & Environment