A corrosion detector for use in detecting corrosion currents in the form of AC and DC leakage currents which occur in a marina. The detector monitors AC power and ground lines or other conductive lines interconnected between boats in a marina and includes a transducer to detect leakage currents which occur in the boats connected to the power lines. The detector provides either an alarm signal or displays the damage rate and location to indicate corrosion currents in one or more of the boats in a harbor.