The humpback spotted splashing in the East River earlier this week has seemingly left the busy channel as quickly as it came — but not without leaving a whale-sized mark on the Big Apple. The US Coast Guard issued a stark warning for boaters to pull back their speeds and leave the cetacean alone, even as some New Yorkers eagerly flocked to the waterfront to catch sight of the beautiful beast. Chris St.

Lawrence was in class at New York University when the 3:45 p.m. alert came through that the whale had kicked its flukes above the surface just below the Brooklyn Bridge.

By the time he made it to East River Park — with binoculars conveniently already stowed in his backpack — darkness had fallen and the humpback had slipped out to deeper waters. “I’ve heard stories of these whales in the past that have wandered into the East River, into the Hudson River, into the harbor, and that’s always been something that I thought would be really amazing to see in person and to get a photo of. And so, I was chasing that dream,” explained St.

Lawrence, 21, the communications lead at south Brooklyn research center Gotham Whale. “It’s not out of the ordinary to see a whale in New York City. It’s crazy to see it in the East River.

” Not ready to give up the dream, the master’s student studying Environmental Conservation Education returned the following morning and spent up to three hours hunkered down on Governors Island, where the whale was also reported to be passing thr.