In a sea vessel having a bilge pump energized in response to bilge water level, an operating parameter of the bilge pump, such as on-time or water output, is monitored and compared with a normal or expected reference value of the parameter to indirectly detect leakage into the bilge. The reference value may be manually set by the operator or may be automatically set in response to circuitry for obtaining the running average of the parameter previously monitored. In one embodiment, an alarm is triggered if the reference is exceeded by the monitored parameter indicative of excessive leakage. In a second embodiment, the monitored parameter is compared with two references. A first alarm at the vessel is triggered if the monitored bilge pump parameter is above the first reference indicating slightly excessive leakage into the bilge whereas a second alarm, which may be remote, is triggered if the monitored parameter is above the second, higher reference indicating grossly excessive leakage.