There are lots of electricity conductors all around us at any given time. As an example, metal, like that of an outboard engine, is a great conductor of electricity. Another strong conducting element is seawater, which your outboard engine in submersed in while boating. Seawater is ... read more a good conductor of electricity unlike freshwater which isn't nearly as good as a conductor. So you see more outboard engine corrosion in seawater rather than freshwater. Other factors of corrosion depend on how much oxygen is present in the water. The more oxygen there is, the better the chance of corrosion; this includes your outboard motor. Areas that seek out oxygen can become anodic and corrode which in turn, damages the metal. Another place that increases corrosion is when pollutants are around. Flow rate can play a part as well. What's also interesting to note is the temperature can increase corrosion rates. Rule of thumb is for every 18 degrees Fahrenheit the rate of corrosion doubles. Therefore, when you outboard heats up, corrosion is vigorously taking place. Last thing that we will mention that affects an outboard engine corroding is bio-organisms. They remove the protection you apply to your outboard, or change your environment into a corrosion-filled one making it really important to have an anode to protect your Mercury outboard. If you have any questions regarding Mercury outboards and anodes, please call 1-800-743-1123 to have all our questions answered.