This resource provides explanations of the key terms encountered when exploring freshwater streams and rivers and native fish. This resource is intended to be used alongside other articles about our freshwater native fish to give a better understanding of some of the key scientific terms used.

Some of the resources you’ll encounter these terms include Stream works for fish, Native fish and the city, Give our fish a hand, Planning for change and Planting stream edges.

Water Safety New Zealand also provides a useful downloadable resource with illustrations on river features.


A loose deposit that can be made up of a combination of soil, sediment, sand, stones and gravel that have been eroded, reshaped by water and redeposited. Alluvian deposits can form features in a river or stream such as a bar or river island.


An adult fish that lives in the sea and migrates into freshwater to spawn. In New Zealand, our only anadromous fish is the lamprey.

Braided river

A river that consists of many channels of water separated by small and often temporary islands called braid bars.


Adult fish that live in freshwater and migrate into saltwater to spawn. Examples of catadromous fish in New Zealand are the native longfin eel, shortfin eel and inanga.


An area where water is collected by the natural landscape. In a catchment, rainwater run-off will eventually flow to a creek, river, dam, lake or ocean or into a groundwater system. The catchment of a waterway is the area of land it collects water from. Understanding the catchment of a waterbody is important when looking at sources of contamination within rivers or streams.


Generally refers to the land alongside a body of water. What banks are made of (soil and rock types), their firmness and the plants that grow there play an important role in what species of fish and other animals can thrive in the stream environment.


An elevated area of sediment within the ocean or a waterbody such as a stream, river or lake. Bars are depositional features formed by the accumulation of alluvium. In a river, continuous deposition and larger deposits such as logs can build up over time to form a more stable river island, allowing for vegetation to begin to grow.


The channel bottom of a stream, river or creek.


A confluence occurs where two or more flowing bodies of water join together to form a single channel.


A general category describing fish that spend portions of their life cycles partially in freshwater and partially in saltwater. Fish are further categorised as catadromous or anadromous depending on what part of their life cycle is spent in saltwater or freshwater.


A circular movement of water causing a small whirlpool (plural: eddies).


The tidal mouth of a large river where freshwater meets seawater. In scientific terms, estuaries are the interface between the land and the sea – the intersection of water, plants and animals. Learn about the different types of estuaries and how they form in Estuary formation.


A wide area within a stream or river with an even flow (of low to moderate velocity) and little or no turbulence. A glide often forms the transition from a pool to the upper end of a riffle.


Usually refers to the starting place of a river or stream – the furthest place in that river or stream from its estuary or confluence with another river.


Relating to or associated with lakes. This essentially means land-locked water bodies such as inland wetlands and deepwater habitats associated with freshwater lakes and reservoirs


A bend in a stream, river or creek.


A description of a river or stream bank that overhangs the water having been eroded or undercut by the water flow. Undercut banks can be dangerous for people but the overhangs provide fish with shelter, a feeding ground or a place for egg laying.


A segment where the water depth is above average and the speed of the water flow (or velocity) is below average.


A section within a river or stream where the water flow is significantly more turbulent. The turbulence and more rapid flow can be caused by an incline of the water bed or other obstacles like rocks.


The length of a stream or river.


A segment in a river, stream or creek where the flow is shallower and more turbulent. Different fish are adapted to live in riffles, such as the endangered dwarf galaxias (Galaxias divergens).


The erosion of the stream bed (vertical scour) or stream banks (lateral scour) by rapid flowing water and the sediments it is carrying. Scour can also threaten fish-friendly culverts by washing away the sediment and gravel that hold the structure in place.


A process by which water becomes dirty as a result of fine mineral particles in the water. When sediment or silt is suspended in water, this is an example of siltation. In New Zealand, our redfin bully (Gobiomorphus huttoni) is particularly sensitive to siltation.


A form of erosion where water cuts away soil from a stream or river bank and leaves an overhang behind. The overhang is often the roots of trees or vegetation.


Water falling from a height, formed when a river or stream flows over a precipice or steep incline.

    Published 13 December 2017