Beaches in one part of Nassau County on Long Island have once again barred swimming following another shark sighting on Saturday.

Officials with the Town of Hempstead alerted beachgoers of the sighting in a tweet that read, "due to a shark sighting by town lifeguards, all swimming is now prohibited at Town of Hempstead ocean beaches from Civic Beach to Lido West beach until further notice."

The alert came hours after Lido Beach reopened, following a reported shark sighting Friday afternoon that prompted police to dispatch their Shark Patrol unit. Lido Beach had imposed restrictions following the sightings, which were once rare but have doubled compared to last year.

At least 11 shark sightings have been reported along the Long Island shores since Monday, forcing an increase in patrols. They've so far responded to even the tiniest inkling of a sighting, as in the case Saturday morning when beachgoers spotted what was believed to be a shark at Zach's Beach at Jones Beach State Park. An extensive search
with the help of a helicopter and boat patrols found nothing, according to Newsday.

Last weekend, a 21-year-old college student TJ Minutillo of Manhasset caught an eight-foot long bull shark at Nickerson Beach, estimated to weigh between 375 and 400 pounds. After snapping a few pictures of the shark, Minutillo set the shark free.

Increased shark sightings have also been spotted in Maine recently, where a Manhattan woman was killed by a great white shark, an incident that is extremely rare in those waters. The woman was identified as 63-year-old Julie Dimperio Holowach, a former vice president of a handbag company. She was killed on Monday morning by the shark that fled, according to the New York Post.

Warmer waters due to climate change could be a contributing factor to all these shark sightings. The Philadelphia Inquirer says, "Sea-surface temperatures continue to run several degrees above long-term averages off the Atlantic Coast. Some of that water vapor over the ocean has migrated to the mainland, which is why it’s been so steamy."

It's one reason, the report says, why the bull shark in Nickerson Beach was spotted: "That species favors subtropical waters."

For now, Nassau County officials have stepped up patrols in the wake of sightings, relying on helicopters and patrol boats to monitor the shores.