The Shedd Aquarium and Forest Preserve are launching a mapping project of freshwater mussels, one of the most endangered groups of animals in North America. An Elgin creek is one of the few places in Illinois where one species of freshwater mussel still lives at all. Once a hot spot for mussel diversity, the population in the Midwest has dropped drastically because of development and invasive species. Freshwater mussels, vitally important to the health of their aquatic ecosystems, are the “livers” of rivers and lakes. Their method of filter feeding removes material from the water, including potentially harmful algae, bacteria and chemical compounds. Mussels also play a major role in shaping the physical features of streams and reducing the probability of severe erosion.