Typically, they have a clearly defined head often with antennae, a thorax and an abdomen, wings and legs may or may not be present. Snails, worms and molluscs are also invertebrates.

Macro-invertebrates refers to a whole range of different species of 'bugs' that live or spend part of their life cycle in water. They are an ideal way to gauge the 'health' of rivers and streams. Different species of invertebrates show various levels of sensitivity to deterioration in water and habitat quality. Generally the poorer the quality of the water, the less diversity of invertebrates that will be found. Some of the more sensitive include mayflies, stoneflies, caddisflies, dragon and damsel flies. Beetles, water boatmen and shrimp tend to have moderate tolerance, and the more tolerant (can survive poorer water quality) include snails, worms, chironomids, blackfly and mosquito larvae.

In some cases the invertebrates observed in rivers and streams will be in their nymph or larval stage, prior to becoming terrestrial adults. In other instances, the invertebrate may spend their whole life cycle within the water

All sections of rivers and streams will contain invertebrates. Different species will show different habitat preferences ranging from fast rapids to still backwaters.

Generally they will eat a range of foods from algae to decaying leaf litter to microscopic organisms living within the sediments, some are predators that prey on other invertebrates. Some nymphs may not feed at all prior to becoming terrestrial. Invertebrates themselves are the single most important food source for most fish species

Poor water quality; Loss of instream habitat; Loss of riparian vegetation