You may have crevis corrosion in the welds on your water lift muffler if it's stainless or a crack in the exhaust hose at some point aft of the muffler, particularly if the hose is very old. As a hose ages, cracks tend to form around the circumference, eventually exposing the wire reinforcing to the air which further weakens the hose. We discoverd the source of a mysterious leak--such a crack in our own exhaust hose--during a cruise to Key West last year. One simple way to check is to soak a small piece of spong in food coloring and place it in the filter basket where debris is collected in your raw water filter. The coloring agent will leach out and discolor the water which will be detectable on a white paper towel. (Whether that is the source or not, don't forget to remove the sponge!)
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."