Lake Michigan surface area is 22,400 square miles and its main depth is 276 ft. Its fauna is generally typical of North American oligotrophic lakes. The original fish populations included 10 coregonines and one salmonine. The lake whitefish, the lake herring, and the lake trout were most abundant. Man's activities have caused great changes in the lake in the past 120 years. Although changes in water chemistry and in the lower biota have been generally modest (except locally), those in salmonid communities have been vast. Exploitation, exotic fish species (especially the sea lamprey and alewife), and accelerated eutrophication and other pollution, all have played a role in bringing about the modifications (mostly marked declines in abundance) in salmonid communities. Commercial exploitation was largely responsible for the changes in the salmonid communities before the invasion of the lamprey (1936), although eutrophication and other pollution, and alterations of spawning streams, also were important. The lamprey and alewife (first reported in 1949), however, have exerted a greater impact than the other factors in recent decades.