Abstract: A water detection plug for use in a marine engine or the like having lubricants such as oil contained therein including an arrangement for indicating the presence of water in the lubricant when the water is in contact with the plug such that the indicator arrangement presents a first distinct visual appearance when not in contact with water and a second distinct visual appearance different from the first visual appearance when the plug is in contact with water, thereby generating a visual signal which is visible to an observer located outside the device when the lubricant in contact with the plug becomes mixed with water.