The US Coast Guard in Boston is sending out a warning to mariners to be cautious of whales that have been seen feeding and splashing around in Boston Harbor over the last few days.

A spokesman said Tuesday that the Coast Guard has received multiple reports about the large marine animals in the area and that a broadcast was going out to boat operators “reminding them to transit with extreme caution.”

The Coast Guard isn’t the only agency keeping an eye on the whales.

Boston Harbor Cruises shared a tweet Tuesday that included a picture of a whale swimming in the harbor.


“Have you heard the news?” the company wrote. “There’s a humpback whale in Boston Harbor!”

Cruise company officials said with so many boats on the water this summer, they are “hopeful that it will return to safer waters soon.”

Sheila Green, a spokeswoman for Boston Harbor Cruises, which takes people out daily on whale-watching expeditions, said naturalists from the company have identified five to six individual whales in the harbor area.

She said one whale has been going back and forth between Deer Island and Spectacle Island, while the rest have been spread out near Boston Light.

“It does happen,” she said of the presence of the whales. “But to have so many in the Inner Harbor is really quite unusual.”

Green said while it’s “nice to see” the whales — an indicator that the harbor is clean — it’s also worrisome.

“It’s a little nerve-wracking,” she said, “because it’s such an active port.”

The Boston Harbor Islands National and State Park also shared an update Tuesday about a humpback whale seen off the city’s coast recently.

In a video posted to its Facebook page, a whale can be seen leaping from the water before crashing back down and creating a large splash. The Deer Island wastewater treatment plant is visible in the background.


“It’s not everyday you see a humpback whale breach from the shores of Spectacle Island,” the organization said.

The island is roughly 4 miles from downtown.

The video was taken by Shane Dwyer, a licensed boat operator with the state Department of Conservation and Recreation.

Dwyer told the Globe in a telephone interview that seeing the whale breach so close to the island Tuesday morning was “a unique experience.”

Susan Kane, DCR’s islands district manager, said she’s been working out on the Boston Harbor Islands since 1996 — and she’s “never seen a whale this close.”

“Everyone here recognized right away that this is really an out-of-the-ordinary thing,” she said.

The sightings this week follow a video taken by fishermen last Friday evening of two whales feeding near the Graves Light.

Steve Annear can be reached at steve.annear@globe.com. Follow him on Twitter @steveannear.