The Grand Calumet River, originating in the east end of Gary, Indiana, flows 13 miles through the heavily industrialized cities of Gary, East Chicago and Hammond. The majority of the river's flow drains into Lake Michigan via the Indiana Harbor and Ship Canal, sending about one billion gallons of water into the lake per day.

The area begins 15 miles south of downtown Chicago and includes the east branch of the river, a small segment of the west branch, and the Indiana Harbor and Ship Canal. Today, 90 percent of the river's flow originates as municipal and industrial effluent, cooling and process water, and storm water overflows. Although discharges have been reduced, a number of contaminants continue to impair the area.

The largest extent of the impairment comes from legacy pollutants found in the sediments at the bottom of the Grand Calumet River and Indiana Harbor and Ship Canal. Contaminants include PCBs, PAHs, and heavy metals such as mercury, cadmium, chromium and lead. High fecal coliform bacteria levels, biochemical oxygen demand, suspended solids, and oil and grease create additional problems. These pollutants originated from both point and nonpoint sources. Nonpoint sources include 5 to 10 million yards of contaminated sediment, industrial waste site runoff, CERCLA sites (five of which are on Superfund's National Priority List), RCRA hazardous waste sites, underground storage tanks, atmospheric deposition, urban runoff and contaminated groundwater. Point sources are limited to industrial and municipal wastewater discharges and combined sewer overflows.