Fish. We don't often see fish, except when we catch them, but the river contains large numbers of fish. Fish have made a remarkable comeback in the years after heavy pollution decimated their populations. Their presence makes it possible for eagles, otters, ospreys, cormorants, herons, mussels, and other species to live in or along the river. Use the checklist below to explore the diversity of fish in the river and explore selected fish species that make up, in part, the great biodiversity of the river.