Abstract: A two pathway exhaust and water discharge through-hull system is coupled to a muffler for separating exhaust gases and cooling water at operating speeds such that at low engine speeds exhaust gases and water are discharged through a first outlet preferably above the waterline and, when the engine speed is increased above a predetermined level, exhaust gases are discharged through a second outlet which communicates with a streamlined, low back-pressure underwater discharge skeg and water is discharged through the first outlet. In a preferred embodiment of the invention, a discharge skeg is positioned at each comer of the transom for a twin engined vessel. In a preferred embodiment also, each of the underwater discharge skegs is mounted to the bottom of the hull and includes a mounting flange and an upwardly extending collar which extends through the hull and is coupled to an adapter for coupling the discharge skeg to an exhaust outlet of a muffler.