A number of other grouper captains credit the boom in bottom fishing to natural factors, namely water clarity. They point out that the water north of the St. Johns River is a bit murkier than south of the river. For that reason, they say, divers are less efficient at spearing grouper and snapper on the ledges, so there are more fish available to hook-and-line fishermen. The theory has merit, since the current here flows north, and a number of rivers pour into the ocean between Mayport and Fernandina. Run-off from the St. Johns, St. Marys, Nassau and other rivers likely clouds the offshore water off Fernandina, which makes spearfishing more viable farther south, most notably off St. Augustine.