the lower fox river watershed monitoring program    
University of Wisconsin Green Bay
University of Wisconsin Milwaukee

Benthic Macroinvertebrates

The benthic (bottom-dwelling) macroinvertebrates supported by a stream are a great indicator of overall stream health due to their variable tolerance of pollution. Generally speaking, mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera), and riffle beetle larvae (Coleoptera) require a relatively pristine environment. Macroinvertebrates highly tolerant of pollution include midge larvae (Diptera), snails (Gastropoda), leeches (Hirundinea), and aquatic worms (Oligochaeta). Organisms such as scuds (Amphipoda), clams (Bivalvia), crayfish (Decapoda), cranefly larvae (Diptera), and aquatic sowbugs (Isopoda), are somewhat tolerant, and are found in a wide variety of water conditions.

Because macroinvertebrates are relatively immobile as compared to other aquatic organisms, they provide a quick snapshot of the condition of their surrounding habitat and the state of the stream’s food web. Macroinvertebrate samples are best taken from within a riffle because the increased level of dissolved oxygen available generally provides the most diverse population of the stream organisms. High diversity and numbers of macroinvertebrates indicate good water quality conditions, whereas presence of only pollution tolerant species or absence of macroinvertebrates suggests a degraded environment. Because naturally occurring coldwater and warmwater streams support different species of macroinvertebrates, researchers should not attempt to compare data from these two types of streams to each other in determining stream health. (spreadsheet of School-based benthic macroinvertebrate Survey Results: 2004-05 NEW)