NORWALK — For the third year in a row, humpback whales have been spotted in Long Island Sound.

After receiving several phone calls from boaters spotting a whale near Cockenoe Island on Friday morning, Westport’s Police Marine Unit headed out to investigate.

When they got close to the island — with cameras rolling — a large humpback whale could be seen surfacing.

Officers made sure the whale was not in distress and kept a safe perimeter around him until he swam into the deeper waters of Long Island Sound. Officers from the Norwalk Police Marine Unit also caught footage of a whale near Peck’s Ledge Light on Friday, which they posted on their Facebook and Twitter pages.

A Norwalk man told Hearst Connecticut Media he saw a whale off Darien while boating after sunset Thursday.

The Maritime Aquarium issued a warning to boaters hoping to catch a glimpse of the massive mammals.

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To watch the video the police shot visit https://www.facebook.com/westportctpolice/?hc_ref=ARRxqizMX1pZYCGy1H_GRKjL3P-z74Zo6KoYdAJjSr6zodpJ33U2UUtGJAjEjkVGDbU&fref=nf

“We do not want everyone in Fairfield and New Haven counties with a boat to go chasing after this animal,” said aquarium spokesman Dave Sigworth in a statement. “Humpback whales are very large animals … bigger than most people’s boats. We do not want boaters hurt and we do not want this whale to be hurt. One of the three humpbacks that turned up in the Sound two years ago was killed ‘by blunt force trauma,’ probably in a collision with a sailboat.”

Sigworth noted that whales fall under the Marine Mammal Protection Act, which places federal restrictions on how closely people are allowed to approach them.

The aquarium encourages anyone who sees a whale to cut their engines or drop their sails, watch and take pictures and video from afar. The aquarium is also asking that any sitings be reported to john Lenzycki and Dave Hudson at the Maritime Aquarium by emailing jlenzycki@maritimeaquarium.org and dhudson@maritimeaquarium.org. There is no electronic monitoring of whales currently being conducted in the Sound.

Whaling was banned in the continental U.S. in 1982, which has lead to a slow population growth in recent years. Whale sightings in the Sound are rare, but data provided by the Maritime Aquarium shows there have occasionally been humpbacks, beluga whales, manatees and pods of dolphins that have made their way into the protected waters. Prior to the 1950s, sightings of marine mammals, specifically dolphins, were fairly common and even expected during the warmer months as more people were on the water or at the shore.

As the water quality has improved, more animals have returned to the Sound, usually during migratory seasons. Experts at the aquarium theorize whales have returned to Long Island Sound the past three years to feed on bunker, which are plentiful this time of year.

Humpback whales can travel hundreds of miles in a day. The whales stayed in the Sound from August to October in 2015 and 2016.

KKrasselt@hearstmediact.com; 203-842-2563; @kaitlynkrasselt