These manatees are gathered at the Tampa Electric's Big Bend Power Station in Apollo Beach, Florida. You can view these manatees from the viewing center located along the discharge canal from the power plant.
When the water cools in a manatee area, the manatees will migrate to areas of warmer water that is 68 degrees Fahrenheit or more. In this case, the temperature of Tampa Bay waters fell below 68 degrees and manatees migrated to this discharge canal where the waters are warmer.
Along with an informative manatee viewing center, this spot also has a tidal walkway where you can see mangroves and many species of birds, fish and other animals in their natural habitat.