Massachusetts shark activity along Cape Cod beaches shut one down Tuesday amid a busy summer season. 

The Sharktivity tracking app showed 14 white shark sightings along the coast over the past two days and four shark detections at buoys. 

There were two detections at Marconi Beach at Cape Cod National Seashore on Tuesday afternoon. 

The app said the shark had been sighted by lifeguards, who closed the beach for an hour to swimmers. 

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"Marconi Beach… 1:30, shark sighting, everyone out of water… 2:30, one hour past since sighting, all clear to return to water. 2:35… shark sighting, everyone out of water!" Facebook user Maureen Cragen wrote in a Tuesday post. "It was like the shark knew when the hour was up."

"Today at Marconi Beach in Wellfleet," wrote user John Cuetara, "we saw sharks… and they saw us."

Earlier in the day, a dead seal was spotted before a white shark was reported a quarter mile off Longnook Beach in Truro. 

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Another shark sighting was reported off of Chatham’s North Beach Island.

"White shark spotted 200 yards off North Beach Island, moving in and offshore rapidly," the Sharktivity post said.

Sharks were also seen off of Chatham’s Monomoy Island, a hotspot for shark activity in the summer and fall, according to The Boston Herald. 

The Sharktivity app was developed with input from the Massachusetts Division of Marine Fisheries, the Cape Cod National Seashore and officials from Cape Cod and South Shore towns.