Yamaha

ZINC - For use in salt water. Not recommended for use in fresh water.
ALUMINUM - For use in salt and brackish water. Performs better, protects longer than Zinc.
MAGNESIUM - ONLY for use in fresh water. Not recommended for use in salt or brackish water. The only alloy proven to protect your boat in fresh water.
Don’t be fooled by claims that only one alloy will protect in all water environments.