Wayward manatee safely back in Fla.

Ilya, an infamous 1,100-pound sea cow, got a lift home in a US Coast Guard cargo plane yesterday after a three-month vacation north, including a late-summer stay off Cape Cod. Rescuers stepped in after the young manatee got lost in a dangerously cold New Jersey river.

“Everything went really smoothly,’’ said Dr. Maya Rodriguez, a manatee specialist and Miami Seaquarium veterinarian, who rode with Ilya on the plane. “He was pretty still, kind of groggy. [Manatees] are very stoic when they’re being transported.’’

The nearly 10-foot-long mammal is now relaxing at the Seaquarium in a warm tank with a new friend, a 2-year-old orphaned female rescued off the coast of Florida a day earlier, Rodriguez said.

“Right away they were touching noses, already hanging out,’’ Rodriguez said. “It’ll be good for him because he hasn’t had company for a while.’’

Ilya probably has not seen another manatee since mid-July, when he was first spotted in the Chesapeake Bay. Over the next two months he meandered up the East Coast, ending up off Dennis and Orleans in mid-September. (Scientists identify him by distinctive notches in his tail.)

Then, after scientists and wildlife officials had assumed he was safely back in Florida’s warmth, Ilya startled a New Jersey oil refinery worker on Oct. 15. He had apparently been lost in the deadly cold waters of Arthur Kill, a river splitting New Jersey and Staten Island. River temperatures were dipping into the 50s, and manatees are in danger of hypothermia in waters cooler than 68 degrees.

“Their immune system shuts down, their intestinal system shuts down,’’ Rodriguez said. “Skin begins fluffing off like frostbite.’’

But Ilya had found a lifeline in a warm tributary, huddling near a refinery pipe discharging 75-degree water.

Wildlife officials quickly converged on the scene, gearing up for a rescue effort. But after a storm delayed the rescue, Ilya slipped away.

“He had wandered off, and we had no idea where he was,’’ said Chuck Underwood, spokesman for the US Fish and Wildlife Service. “Then earlier this week, he showed back up.’’

Within three days, rescuers had Ilya at the Atlantic City airport, loading the half-ton beast onto a Coast Guard plane.

“We do training flights routinely, and this was an opportunity to do pilot training . . . as well as fulfill our statutory obligations,’’ Coast Guard spokeswoman Lorraine Brooks said.

Rodriguez said Ilya was in good health, considering his exposure to the cold. And at 10, he has 50 to 80 more years to live. She expected him to be released within weeks.

But she cannot say for sure why he wandered off on an estimated 2,000-mile journey.

It may be global warming or population expansion, she said, but most likely it’s just curiosity.

“Some of these males go exploring during the summer. They venture out, looking for new mating herds, following females,’’ Rodriguez said. “They’re what we call pioneers.’’