A manatee that took an unheard-of swim 700 miles up the Mississippi River eluded a rescue team Thursday that hoped to return the animal to the sea.

The animal, about 8 feet long and 1,000 pounds, has been hanging around since at least Sunday in a three-mile channel along the downtown riverfront.

Rescuers, including marine biologists and Coast Guardsmen, began searching the channel early Thursday and quit in the evening, planning to return Friday.

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The manatee was last seen Wednesday.

"It's never been recorded before this far up the Mississippi," said Pedro Ramos, a team leader from SeaWorld of Orlando.

Manatees are found mostly along the Gulf of Mexico and the Atlantic Coast, from Alabama to South Carolina.

Sometimes they stray farther north; this summer one made it as far as New York City.

Ramos said his team would search the 60-degree water at least through Friday, using boats and a police helicopter.

"We can't just stay up here indefinitely," he said. "As long as he's eating he could probably survive for a few days. It will really depend on the water temperature."

Manatees are plant eaters, but the searchers also were unsure whether vegetation along the channel would supply the animal with the nutrition it needs.

The rescue team hoped to net the manatee, load it on a truck, keep it wet between pieces of foam and take it to SeaWorld for medical tests and rehabilitation before releasing it along the Florida coast.