Stream Invertebrates

This page details the importance of invertebrates - animals without backbones - when assessing stream health.

Invertebrates include all insects, snails, crustaceans and worms. Freshwater crayfish (koura) are the largest invertebrate living in Tasman streams.

The larvae of many insects, such as mayflies, stoneflies and caddisflies, spend most of their life in streams and rivers, but their short adult life is out of the water.

Council uses the number and type of invertebrate species found in streams to assess stream health, for example:

• Mayfly, stonefly and caddisfly larvae are found in streams with high quality habitat, for example, in the headwaters of catchments covered in forest.
• Snails and worms are more common in degraded streams and rivers, especially those in the lower catchments where there is urban or agricultural development.

About 30 percent of Council’s monitoring sites in developed catchments are either moderately or severely degraded. These streams are often in smaller catchments and in urban areas where streams can contain heavy metals and more sediment, or in agricultural catchments where vegetation clearance and land development has caused increased water temperatures and greater accumulation of silt on the streambeds.