(CNN) — Manatees weigh half a ton and range up to 13 feet long. You don't.

While they like to munch on underwater plants, you might prefer a nice wedge salad, or perhaps a slice of pizza.

But there is one way you and Trichechus manatus are probably a lot alike: Neither one of you likes being cold.

So, as often happens this time of year , the U.S. Fish and Wildlife Service has been forced to close off water access to Three Sisters Springs in Crystal River, Florida, as hundred of manatees seek protection from the chilly waters of the Gulf of Mexico.

And what a sight it is -- nearly 400 of the burly marine mammals crowded into the serene 72-degee waters of the springs, likely dreaming of spring and warmer days to come.

"It's almost like a bear hibernating in a cave," Ivan Vicente, a visitor services specialist with the Fish and Wildlife Service, told CNN on Tuesday.

"They do sleep for over a whole day. When they do wake up, there's very minor movements and very little activity, and then they just go back to sleep," he said.

This is serious business: Cold stress can be fatal for manatees, and even the ones at Three Sisters Springs and other wintering spots can lose a lot of weight.

So even though the manatees may soon be removed from the endangered species list, state and federal wildlife officials are pretty strict about protecting them during their winter snoozes.

That's why the springs -- a key cold-weather go-to for the manatees -- are closed to humans when too many chilly manatees come calling.

The springs are a popular destination for kayakers, canoeists and snorkelers wanting to boat or swim with the gentle animals.

The site will remain closed through Tuesday, at least, but could reopen Wednesday when high winds and a cold front are expected to relent and allow the tide to go out, Vicente said. The manatees will then swim over to another warm spot, he said.

But with more cold weather forecast, wildlife officials predict the number of manatees sheltering around the springs could again jump as high as 500, rivaling records set in the state's 2010 cold snap, and forcing another closure.