A marine cathodic protection system configured to protect a metal structure exposed to seawater from corrosion. The system includes a first anode provided on or adjacent the protected metal structure at a first position. The first anode is exposed to seawater, is electrically insulated from the protected metal structure, and is formed of a metal having a greater negative potential than the protected metal. The system further includes a second anode provided on or adjacent the protected metal structure at a second position. The second anode is electrically connected to the first anode. The first position is preferably substantially submerged in said seawater such that the protected metal and the first anode cooperate to define a seawater battery configured to apply an electrical current to the second anode, the second anode thus being an impressed current anode.