Originally Posted by C4ENG
On the galvanic chart series, magnesium is least nobble from Zinc which means the magnesium will then sacrifice itself to protect any zinc installed on the vessel making the zinc a more noble metal in that situation.
Fresh water does carry less TDS to carry electric currents and atoms to flow through but I would be interested to know why or how magnesium could sacrifice itself better than zinc to preserve the more noble metals just because it is in fresh water oppose to salt water.
If you can overcome the sales pitch there is some good info to be found here. Cathodic Protection - Marine Cathodic Protection - MGDUFF