Coho occur naturally in the Pacific Ocean from California to Alaska. They have also been successfully introduced into the Great Lakes. Coho spawn in cold, clean fresh-water rivers anytime from September until February. The young hatch and remain in the stream for almost 18 months before leaving for life in the big water. In both the ocean and Great Lakes, coho wander at random following baitfish. By late summer of their third year, most coho return to the mouths of their home river where they continue to pack on weight until cool rains attract them upstream.