[5] The Grand Calumet is divided into an East and West branch, on the respective sides of the Indiana Harbor Canal.

The East Branch, which drains entirely into Lake Michigan,[6] rises in Marquette Park in Gary's Miller Beach neighborhood, passing through a series of three lagoons - two of which are partially located within the Miller Woods unit of Indiana Dunes National Park - before flowing through the industrial zone of Gary.

[7] In addition, the Indiana Harbor Canal itself is sometimes treated as a part of the Grand Calumet, which brings the river's total length to 16.0 miles (25.7 km).

[13] The construction of the Gary Works in 1905 involved diverting and channelizing a considerable part of the East Branch to make way for the new steel mill.

[14] Previously, the Grand Calumet had flowed across a large part of the present-day mill site, and spread to 1,000 feet wide during floods.

As of 2015, a major dredging project was under way to remove several hundred thousand tons of toxic sediment from the bottom of the Grand Calumet.

"[18] Only sludge worms inhabit the Indiana Harbor and Ship Canal, indicating that severe pollution exists.

Additional problems include high fecal coliform bacteria levels, biochemical oxygen demand (BOD) and suspended solids, oil and grease.

[20] Fish populations in most of the Grand Calumet were virtually wiped out in the 20th century, although the headwaters area continues to support sensitive native species including the Iowa darter.

[22] Known as the Tolleston Strand Plain, the preserves are home to the dune and swale habitat, which once covered large areas around the Great Lakes but is now considered globally rare.

[22] Other rare species include the Franklin's ground squirrel, Blanding's turtle, the glass lizard and the black-crowned night heron.