Not really a swamp, but it has some similar characteristics. You can find this along one of the hiking trails at Lake Louisa State Park.
Dark water warning at Lake Louisa State Park. The tannins from the vegetation leave the water a lovely shade of dark brown (some say tea colored). Since you would not be able to see a submerged person they have this warning for all swimmers.
The Van Fleet State Trail is a Rail-to-trail that runs 29 miles from Sumter County down to Polk County. There are three trail heads, one at each terminus north and south, and a main entrance off of County Road 565 in Lake County. You will occasionally see remains of the rail line that ran through here. Learn more about the Van Fleet State Trail here https://www.floridastateparks.org/trail/Van-Fleet.