Yup, here in Florida at least. Where I used to live they'd come into the canals and lagoons all the time. They seriously are water fat doggos.

They bounced back for multiple reasons.

1. No wake zones (slow boat) in areas that are prone to having manatees, that being said… I've still yet to see a single manatee without a prop scar.
2. Getting people to stop giving them fresh water. Fresh water is like candy to them since they are salt water animals. People would drop their hoses in the water and the manatees would literally drink until they could not float anymore and drown (they have smooth brains, AKA they are very dumb). Even if they did not sink if they drank it long enough their bodies would ozmoregulate to be fresh water. And when the hose was taken out of their mouth they'd get killed by the salt water. (like throwing a freshwater fish in the ocean)
3. And this is a big reason, Power plants. Yup. The water they used to cool off the reactors would drain into the sea and is very warm. So manatees would horde at the power plant's drain basin to warm up to survive the winter, because Florida's water still get too cold for the big guys. (Their blubber is for flotation, not warmth) Heading south to the Keys or going to warm caves is the natural way they survived the winter so the Power plants gave more places for manatees to hide, so less died in cold snaps.

That last point reminds me of the time Homer swapped himself for a manatee at the power plant, and Mr Burns and Smithers took great care of it.