• After the glaciers retreated about 10,000 years ago, some of the potholes in the Chicago region developed into wetlands, including swamps and bogs.

Most of these wetlands and wet prairies have been drained for farming and settlement.

The Chicago Portage plays a major role in human development and ecology of the region.

• The Chicago Portage is a narrow strip of land separating the Des Plaines River (which drains to the Mississippi River and the Gulf of Mexico) and Lake Michigan (connecting to the Atlantic Ocean via the St. Lawrence Seaway).

This continental divide was breached in 1848 by the Illinois and Michigan Canal, later replaced by the larger Chicago Sanitary and Ship Canal in 1900.

The canal allowed for diverting water from the Chicago River, reversing its flow so that now it drains away from Lake Michigan.

• Potholes (kettles) were created when retreating glaciers left behind chunks of ice sitting in a depression, which eventually melted to yield freshwater ponds and wetlands.

Glacial potholes can be observed in some DuPage county forest preserves: Herrick Lake in Wheaton, and West Chicago Prairie.

• Wetlands are shallow freshwater pools where the soil is saturated with water.

Water-loving plants such as cattails and amphibians such as Tiger Salamander find habitat here.

• Marshes

• Swamps

• Bogs

• Vernal pools

• Swales

• Marshes are dominated by herbaceous (non-woody) plants that can grow above the shallow water.

Some plants include Common Water Plantain (Alisma subcordatum) and Blue Flag Iris (Iris virginica).

The Red-winged Blackbird nests among the cattails in spring, each colorful male staking out and aggressively defending its territory.

Mosquito larvae thrive in the stagnant water.

Frogs that can be found here include

• Greenfrog
  call:
• Bullfrog
  call:
  alarm:

• Swamps are forested wetlands where woody trees such as Swamp White Oak Quercus bicolor) may grow.

Herbaceous plants include Swamp Milkweed (Asclepias incarnata).

• Bogs are covered in floating mats of sphagnum moss.

Acidic conditions slow decomposition, and each moss generation builds upon dead tissue of previous generations.

Layers of dead moss are compacted into peat that can serve as soil thick enough to support trees such as Tamaracks.

Birds such as Sandhill Cranes (Grus canadensis) may nest here, feeding on vegetation and small animals.

• Vernal pools are depressions deep enough to collect seasonal rain.

They may fill with rain water in the spring and are valuable breeding grounds for fast-growing amphibians such as this Spotted Salamander.

The adult female lays eggs in the vernal pool in spring, and the pool must remain wet enough for the hatched larvae to complete their juvenile development before the pool dries up in the summer.

• Swales are artificial low-lying depressions with vegetation that can absorb storm water.

They work best if planted with moisture-loving plants such as Prairie Cord Grass (Spartina pectinata).

• Prairie potholes are "duck factories"; the diversity of pothole types provides varied feeding grounds for the two major groups of ducks.

• Dabblers such as Northern Shoveler and Mallard (Anas platyrhynchos?) are surface feeders, sometimes "tipping up" to forage on the shallow bottom.
  • Mallard female:
  • Mallard male:

• Divers such as Common Merganser, Eared Grebe, and Double-crested Cormorant can dive under water and swim after prey in deeper water.

• Many insects inhabit freshwater habitats.

• Daphnia ("water fleas") are microscopic crustaceans near the bottom of the food web.

• Water Boatman uses long rear legs as "oars" for swimming.

• Backswimmer also has "oars", but swims upside-down, and many have red eyes.

• Water Strider can walk on water, using wave vibrations for communication.

• The retreating glaciers left behind a large kettle - Lake Chicago, called Lake Michigan today.

Over the course of thousands of years, water levels subsided as new outlets opened.

For example, the Chippewa stage saw a big drop in lake level as a new outlet opened in Ontario.

Temporary rising occurred in the Early Nipissing as the ice continued to melt.

The retreat of the heavy ice sheet also caused the earth's crust to rise; this "geostatic rebound" continues to elevate the whole area, and Lake Michigan continues to shrink through its outlets.

• The Great Plains in the U.S. lie within the Missouri River and Mississippi River basins.

Moving water in rivers and streams provide more oxygen to sustain fish and other wildlife such as Northern Leopard Frog (Rana pipiens) and Great Blue Heron.

Insects such as mayflies, dragonflies, and damselflies spend their juvenile stage in streams, and serve as living indicators of water quality.

Many streams, including the DuPage River, have been channelized for navigation and irrigation, losing their value as wildlife habitat.

• This Mayfly is molting from its aquatic juvenile (nymph) stage.

The nymph is adapted to living in a stream with moving water.

The nymph molts twice to take on this adult form, lives for a few hours to breed, then dies.

• Dragonflies and damselflies belong to the insect order Odonata, with aquatic larva (nymph) and flying adult life cycles.

Dragonflies such as Eastern Pondhawk may spend 1 to several years as nymphs before emerging as adult.

Other dragons commonly seen on the COD campus include Widow Skimmer and the constantly flying Black Saddlebags.

Damselflies such as American Rubyspot, and Ebony Jewelwing also have an aquatic nymph stage.

Other damsels commonly seen on the COD campus include Eastern Forktail and Spotted Spreadwing

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• Odonata perform unique mating behaviors.
  • The partners form a mating wheel resembling a valentine.

    Male produces spermatophores in segment 9 and stores them in segment 2.

    He grasps the female behind her head with claspers located in segment 10.

    The female then curls her abdomen to dock with his segment 2.

    Before fertilization, he scrapes out any spermatophores in her genitalia from previous matings.

    Female deposits eggs in water using her ovipositor, often into herbaceous stems.