The call went out around 4 p.m. at Mayo Lake, which is part of Mayo Park.
Officials said the man -- who appeared to be in his 50s -- was on a pontoon boat with several friends when the boat broke down. Another boat towed the boat within 20 yards of the shore.
The man jumped in the water to swim to shore and never surfaced.
Officials say he drowned in 7-8 feet of water.
No other information was released.