grew rapidly and came to dominate the Midwest and greatly influence the nation's economy. The Chicago Union Stock Yards dominated the packing trade. Chicago became the world's largest rail hub, and one of its busiest ports by shipping traffic on the Great Lakes. Commodity resources, such as lumber, iron and coal, were brought to Chicago and Ohio for processing, with products shipped both East and West to support new growth. Lake Michigan—the primary source of fresh water for the city—became polluted from the rapidly growing industries in and around Chicago; a new way of procuring clean water was needed. In 1885 the civil engineer Lyman Edgar Cooley proposed the Chicago Sanitary and Ship Canal. He envisioned a deep waterway that would dilute and divert the city's sewage by funneling water from Lake Michigan into a canal, which would drain into the Mississippi River via the Illinois River. Beyond presenting a solution for Chicago's sewage problem, Cooley's proposal appealed to the economic need to link the Midwest with America's central waterways to compete with East Coast shipping and railroad industries. Strong regional support for the project led the Illinois legislature to circumvent the federal government and complete the canal with state funding. The opening in January 1900 met with controversy and a lawsuit against Chicago's appropriation of water from Lake Michigan. By the 1920s the lawsuit was divided between the states of the Mississippi River Valley, who supported the development of deep waterways linking the Great Lakes with the Mississippi, and the Great Lakes states, which feared sinking water levels might harm shipping in the lakes. In 1929 the U.S. Supreme Court ruled in support of Chicago's use of the canal to promote commerce, but ordered the city to discontinue its use for sewage disposal. New construction boomed in the 1920s, with notable landmarks such as the Merchandise Mart and art deco Chicago Board of Trade Building completed in 1930. The Wall Street Crash of 1929, the Great Depression and diversion of resources into World War II led to the suspension for years of new construction. The Century of Progress International Exposition was the name of the World's Fair held on the Near South Side lakefront from 1933 to 1934 to celebrate the city's centennial. The theme of the fair was technological innovation over the century since Chicago's founding. More than 40 million people visited the fair, which symbolized for many