An exhaust system for a marine exhaust system includes two identical liquid-cooled exhaust manifolds. Each exhaust manifold has an outlet portion adapted to receive and retain a catalytic converter. Liquid cooled first and second risers are secured to the first and second exhaust manifolds. Bypass hoses enable fluid to pass from each exhaust manifold to its coupled riser. At the outlet of each riser, the cooling fluid and exhaust gas mix in a Y-pipe to create a combined flow. An exhaust outlet conduit downstream of the Y-pipe receives the combined flow and discharges the combined flow.