Incredible video shows manatees gathered at Three Sisters Springs in Crystal River, Florida Sunday morning.
Air temperature at dawn was 30 degrees Fahrenheit compared to 73 degrees Fahrenheit in the spring.
Cold weather can weaken manatees' immune systems and eventually kill them.
Adult manatees can weigh up to 1,200 pounds and grow to be 10 feet long. During the warmer months, manatees leave Florida and can be found as far west as Texas and as far north as Massachusetts - although sightings along the Gulf Coast and near the Carolinas are also common.
The Associated Press contributed to this report.