(CNN) — Florida's Three Sisters Springs got a little crowded this week when more than 300 manatees swam quickly into the springs, prompting park officials to close the springs to human swimmers and kayakers.
Up to 600 manatees winter in Florida Kings Bay and Crystal River from November to March, but the population drops to 30 manatees the rest of the year. The warm waters of Three Sisters Springs, part of Crystal River National Wildlife Refuge, allow manatees to live safely during the winter months, when the open waters can get dangerously cold for the gentle mammals.
About 80 miles north of Tampa, it's also a popular place for visitors to see and swim with the manatees.
Three Sisters Springs is the only "confined-water body in the United States" open for the public to see wintering manatees, according to the U.S. Fish and Wildlife Service, which manages Three Sisters Springs for the city of Crystal River and the state.
Though the springs closed Monday and reopened Tuesday, the refuge's policy is to close them again as needed.
Noting increasing manatee harassment at the springs since 1979, the U.S. Fish and Wildlife Service has been considering a policy to restrict access to the manatees during the winter months.
"Swimming with manatees is a tremendous experience, and I know that when done properly, everybody benefits," said Andrew Gude, who manages Crystal River National Wildlife Refuge, as well as Lower Suwannee, Cedar Keys and Chassahowitzka National Wildlife Refuges, in a December statement. "It is the experience of a lifetime."
This isn't the first time animals simply living their lives have crowded out their human visitors.
Harbor seals take over Children's Pool beach in the San Diego suburb of La Jolla for five months each year during pupping season.
After years of visitors bothering the seals at the small beach in the tony neighborhood, the beach has been closed to humans from December 15 to May 15 under a San Diego City Council plan approved in 2014 by the California Coastal Commission.
No matter what modest restrictions were put in place in the past, visitors would still bother the birthing seals, officials said, leading to the possibility that scared mother seals might abandon their pups.
"Every time we've tried to help both the people and the seals, it hasn't worked out," Coastal Commissioner Dayna Bochco told the Los Angeles Times. "If more people would act reasonably, we wouldn't be here today."
Though swimmers and snorkelers protested the move, many day trippers have preferred to admire the animals from afar. The seals' tendency to defecate where they live can make the waters unsanitary for human swimming.