Disclosed herein is a marine propulsion device which comprises an engine having an exhaust port for discharging exhaust gas, and which also comprises a lower unit having an exhaust tube in communication with the exhaust port. The lower unit includes a cavitation plate submerged in water during idle engine operation, and an exhaust outlet in communication with the exhaust tube. The exhaust outlet affords discharge of the exhaust gas below the cavitation plate. The lower unit includes an outer wall including an outlet, which outer wall outlet is located above the cavitation plate and submerged in water during idle engine operation. The lower unit also incudes a passage in communication with the exhaust tube and the outer wall outlet. The passage affords, during reverse engine operation, discharge of a portion of the exhaust gas from the exhaust tube out the outer wall outlet.