There should be a green ground wire that connects all the metal to the keel. Life lines, mast, engine, shaft etc
Did anything change in your dock neighborhood? I had a couple of years where my zincs looked a little sketchy then it went away after I got a couple of new neighbors. I suspect one of their shore power systems was “leaking” current into the water and it was finding it way back through mine. They moved and suddenly my zincs come out of the water looking like new
PSA - never swim in a harbor for this very reason. Electro shock drowning
