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Phones with the Sharktivity app were buzzing on the regular for the first time this season on July 15.

Shark alerts were coming in often during the afternoon, as people reported that they saw great white sharks off Chatham.

"White shark spotted 40 feet off North Beach Island (Chatham)," reads the shark alert on the Atlantic White Shark Conservancy's Sharktivity app.

An apex predator was also seen 20 yards off North Beach Island, heading south.

"It's a busy afternoon off of North Beach Chatham," posted shark researcher John Chisholm, an adjunct scientist with the New England Aquarium. "Be #SharkSmart and download the Atlantic White Shark Conservancy #Sharktivity app to stay informed on… White Shark sightings and alerts."

Chatham is a hotspot for great white sharks. The sharks hunt for seals in the area.

Shark alerts are issued when a white shark sighting is confirmed close to a public beach. A notification goes out with each alert.

The Atlantic White Shark Conservancy's 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 to raise awareness of the presence of white sharks.

The app sightings are fed by researchers, safety officials, and users that upload photos for confirmation.

"By enabling App users to report shark sightings and upload photos for confirmation, we are effectively crowd-sourcing critical data points on where sharks are spotted so as to reduce encounters and promote safety," reads the Conservancy's website.

Data from sharks with acoustic tags and Smart Position and Temperature Tags (SPOT) are also available on the app.

Public sightings submitted through Sharktivity are verified by the New England Aquarium.