Three Sisters Springs, a wildlife refuge of warm-water springs in Crystal River, Florida, had to close on Monday and for half-a-day on Tuesday after being invaded hundreds of manatees.

WTSP-TV in Tampa Bay reports  the marine giants are welcome at the springs, which are a natural refuge. Manatees migrate from the Gulf of Mexico annually in the fall to rest and feed in the warm waters, and the springs are part of the Crystal River National Wildlife Refuge where tourists can visit to canoe, swim, walk and view the gentle, slow-moving creatures. 

When more than 300 manatees suddenly entered the springs, however, the U.S. Fish and Wildlife Service asked the park to close for the animals' protection as per the agency's standard policy.

It isn't unusual for a high amount of manatees to periodically enter the warm springs during cold weather, according to the park.

"Because manatees don't have any blubber to help them stay warm, they have to come into these warm water springs to stay warm," Kimberly Sykes, assistant manager of the Crystal River National Wildlife Refuge, told WTSP-TV. "If not, they could get cold-stress and die."

This is not the first time manatees have visited the park by the hundreds.

"We've recorded over 580 in the springs at one time," Sykes explained.

Manatees are protected in the U.S. under the Endangered Species Act. Protecting their habitat is a top priority for Florida wildlife managers. 

While it may seem extreme to close the park, it is necessary to keep the refuge free of turmoil so the marine animals can rest and get warm. For example, on Dec. 27, Sykes said there were 842 swimmers and 340 boaters at the springs.

On Tuesday, the springs reopened at 10 a.m. but had to close again at 2 p.m. It opened again Wednesday at 10 a.m., and Sykes expects it to stay open all day.

The manatees can be unpredictable.

"We're just assessing it on a daily basis," she said.