Passengers on a whale watch off Cape Ann were treated to the rare sight last week of the world’s largest animal species.

Staff with Cape Ann Whale Watch wrote on Facebook that during an excursion on July 4, a blue whale was spotted. 

“​​We had heard the rumors but wouldn’t allow ourselves to get our hopes up,” Tina McMahon, head naturalist for Cape Ann Whale Watch, wrote. “As we were scanning the area for whales, we spotted a blow (whale exhale) taller than a two-deck whale watching vessel. Could it be? We spent the most extraordinary 30 minutes in the presence of a BLUE WHALE!!!!!”

McMahon said she’d only seen a blue whale, the world’s largest animal, one other time, more than 20 years prior. Blue whales, which are endangered, can eat up to six tons of krill a day and weigh as much as 200 tons. 

According to the World Wildlife Fund, a blue whale’s heart is the size of a Volkswagen Beetle.

McMahon wrote that the first time she saw a blue whale decades ago, it was only to see it surface and then dive below the water.

“This blue whale was doing 4-minute dives and we [were] able to see the whale’s EXTREMELY long body under the surface and it nearly fluked,” McMahon wrote of Thursday’s sighting. “I did note that this whale looked quite lean; I could visibly see its ribs and could count the vertebrae on the peduncle.”

Seeing the giant animal had passengers on all the whale watch boats cheering to one another as the vessels took turns in the area, McMahon said.

“One single animal ignited a sense of camaraderie between strangers…lessons to be learned from nature,” she wrote. “I cannot guarantee that we will encounter this individual on any other trip but what I can share is that being in the presence of wildlife reminds us that we share this planet and how absolutely awesome Earth truly is.”