The majority of Illinois' Large streams and rivers can be categorized as lower perennial. Permanent water usually flowing over a bottom of silt, sand, clay, or fine gravel, and a well developed floodplain characterized this type of wetland. As in the upper perennial streams, there are not named soils in this community.

Oxygen deficits sometimes occur, and true planktonic organisms exist. Faunal diversity is largely dependent on water quality, with the more heavily polluted streams supporting less variety. Wetland vegetation consists mostly of rooted emergents, with floating leaved or submerged vascular plants and algae occurring rarely. Extensive wetland marshes, swamps, or bottomland forests may be found along the perimeter, or within the channel of the stream, but these areas will be classified in the palustrine system when the vegetation comprises greater than 30% of the areal cover, and the area is dominated by trees, shrubs, persistent emergents, emergent mosses, or lichens.

*Used throughout the community descriptions to indicate the most commonly occurring code in Illinois

Lower Perennial Stream