The most common animals in the Mississippi Valley are mink, muskrats, opossums, otters, and skunks. This area also provides winter nesting grounds for ducks, geese, and other migratory birds. Pelicans, herons, and egrets live in the area throughout the year. Forests of hardwood trees, such as basswood, hickory, maple, and oak, grow in the upper Mississippi Valley. South of Cairo, the forests consist mainly of baldcypress, sweet gum, southern oak, and tupelo trees.
Pollution seriously threatens the wildlife of the Mississippi.
Fertilizers and insecticides used on farms are washed into the river, and industries empty wastes into its waters. Since the 1970's, steps have been taken to prevent further pollution of the river. For example, federal regulations prohibit farmers from using certain insecticides and other harmful chemicals. The Mississippi was formed about 2 million years ago at the beginning of the Pleistocene Ice Age. During this period, glaciers covered much of the Northern Hemisphere.