The wetlands function as a seasonal fish nursery for Lake Ontario, and despite the historical degradation, most historical species of fish can still be found using the marsh. As with birds and plants the location is a biodiversity hotspot for Canada with over 60 species present. Each spring thousands of spawning fish migrate in through the Fishway from the bay and lake, laying eggs and leaving shortly after, allowing the marsh to function as a giant fish hatchery. Annually between 5 and 20 million fish are produced for the lake depending on water levels and water pollution events. The species present reflect the degraded marsh habitat with the most common the gizzard shad (formerly carp). Also common are night time predators species channel catfish and brown bullhead, along with invasive species such as alewife and white perch. Popular angling species present in limited numbers include pike, largemouth bass, and yellow perch, but the large adults are only present in the marsh during the spawning season which is closed to fishing. The spring and fall season also brings several migrating salmon and trout to the marshes main inflowing river.