Macroinvertebrates

Macroinvertebrates are any animal lacking a backbone, and are generally visible to the unaided eye. In rivers and streams, these are primarily aquatic insects, but may include clams, mussels, snails, crayfish, and crabs, among others. They are are extremely valuable as water quality study subjects because:

They are unique
Each species has specific requirements for survival. Some need water with a high dissolved oxygen content, or they may have low tolerance to toxic pollutants, while others may withstand low oxygen levels and may be highly tolerant of toxic pollutants.

They are easily collectible
Most macroinvertebrates move relatively slowly and are often attached to various surfaces on the stream bottom, making them easy to collect.

They reflect past conditions
While chemical tests indicate water quality at the moment of sample collection, changes in water quality may go undetected between samplings. Because these organisms live in the same area for most of their lives, macroinvertebrate communities can document water quality conditions over the past few months.

With this in mind, the overall health of the stream can be indicated by the presence or absence of pollution sensitive organisms and the diversity of species collected. High diversity indicates a stable and healthy ecological system.

Macroinvertebrate Water Quality Indicators

Stoneflies (Order Plecoptera) All stonefly nymphs have a roach-like body, two tails, and two hooks at the end of each leg. The nymphs can reach up to 1 inch in length. They live in fresh water and indicate EXCELLENT water quality.	NymphAdult
Mayflies (Order Ephemeroptera) All mayfly nymphs have a roach-like body, two or three tails, and one claw at the end of each leg. Rows of gills can often be seen along the sides of the abdomen. They live in fresh water and indicate GOOD water quality.	Mayfly Nymph
Caddisflies (Order Trichoptera) All caddisfly larvae have a maggot-like body, six distinct legs, and two hooks at the end of the body. Many camouflage themselves in cases made from pebbles and debris fastened by silk to the underside of rocks. They live in fresh water and indicate FAIR water quality.	Caddisfly larva & case (up to 1" in length)
True Flies (Order Diptera) All true flies have a maggot-like body and lack distinct legs. They live in fresh water and indicate POOR water quality.	Black Fly larvae (up to 1" in length)