Caño Negro is a seasonal lake/wetlands/everglade system that is fed by the Rio Frio. Tarpon can be found here year round, but as I mentioned earlier there is an increase in tarpon in the river systems from December until May, at which time many return to the ocean.
There are monsters to be had in Cano Negro and on the Rio Frio. In fact, I read an account of a 7 ft 1 inch giant weighing 205lbs that was caught in 2003. However, there is a greater concentration of juveniles in Cano Negro than on the coast: average fish are in the 30-40lb range versus the 80lb average for tarpon on the Caribbean. Also, the big tarpon here tend to be a coppery color instead of bright silver due to the high concentration of tannins in the water.