Lakes & Ponds

Walking trails in northern Illinois are found among many lakes and ponds.  Over time, these bodies of water have  formed and disappeared at varying rates, providing habitats for wildlife and vegetation. 

Several types of water features were formed by the action of the last glaciers that left this area about 13,000 years ago.  Kettle lakes were created when large blocks of ice, buried in the rocky edges of retreating glaciers, finally melted, leaving a hole filled with water.  Surface lakes also resulted from glacial debris  blocking off rivers and streams. 

During heavy rainfall, some rivers collect enough water to force a new flow straight through the landscape leaving an older channel cut off into an oxbow lake.  As rivers slow and shrink, beavers move in to dam them and create new ponds.  Limestone lies under much of Illinois topsoil, dissolving slowly in running water, opening up sink holes that quickly fill to form new lakes.

Ponds and lakes constantly gain and lose water.  Water comes in from rainfall, rivers and streams, groundwater, and springs.  Water is lost through rivers and streams, groundwater aquifers, and evaporation.  Incoming water often carries mineral and organic sediments, slowly filling in the basin.  In areas where shorelines are not exposed to wind and wave action, seeds floating on wind and water will begin to take root.

Ponds and lakes come in many sizes, with shorelines that gradually recede to deeper water or fall off quickly.  On the surface, water molecules are attracted to each other to form a firm layer between the  water below and the air above.  Some organisms use the top side of the surface layer to land on, float on, or run across.  Insects, snails, and microorganisms hang off the underside of the surface layer.  Where sunlight penetrates, water layers are teeming with single-celled green organisms providing an abundant food source for aquatic wildlife.  Shallow lake bottoms support emergent plants, rooted in bottom soil and sending shoots above the surface for air and sunlight.

Reeds, grasses, and other marsh vegetation colonize shorelines and shallow areas.  Tall vegetation catches and traps wind-blown particles.  Sediment comes in from streams and rivers running through the vegetation, gets filtered out and added to the soil layers.  As more plants grow on the edges, and soil deposits become denser, woody shrubbery start to move in.  Given time, in a natural process, existing lakes and ponds will become ever smaller.

Many lakes and ponds are affected by human activities, slowing down the natural cycle.  Dredging and removal of edge vegetation reduces the amount of accumulated sediment.  In urban areas, open ground that used to catch rainwater and allow it to slowly filter into wetlands is being covered with impermeable surfaces including roads, buildings, and parking lots.  Increased runoff from these surfaces flows quickly into existing lakes and out again just as fast, keeping vegetation from getting an anchor. 

As you wander the trails, be sure to observe the differences in lakes and ponds of all varieties, and the many plant and animal species supported by each.