Aquatic habitat
A habitat is the physical environment in which a plant or animal (or community of species) is usually found. The habitat preferred or required can change through time as some animals need to move to different habitats during different life stages. 
Aquatic habitats occur at a range of scales, from a micro-habitat under a particular log to a macro-habitat such as a pool or riffle and, at the broadest scale, to the entire river system.
Typical habitats include bed substrate such as silt, sand, clay, stone, rock; aquatic and riparian vegetation; debris from vegetation such as leaf litter, twigs and logs; areas of different water quality, depths and flow speeds such as pools, riffles/rocky rapids and backwaters. Some plants and animals require floodplain habitat and some animals need to move along the length of a river system (see barriers to aquatic connectivity).
As different species of plants and animals require different habitats, the presence and condition of aquatic habitat in a waterway has a major influence on the species and communities found, and hence on the health of a waterway.
For example, large woody debris provides a stable surface for macroinvertebrates, particularly in sandy waterways where the surface can be unstable. It also provides a surface for aquatic plants and algae which absorb nutrients from the waterway and provide a source of food for macroinvertebrates. Woody debris slows the speed of water, creating shelter from faster flowing water for macroinvertebrates and fish, and also provides protection from predators and heat from the sun. Debris that emerges from the water provides roosting and preening sites for birds. Water Note 9 provides further information about the value of large woody debris and snags.
The following documents provide information about the importance of habitat to waterway health and how to manage aquatic habitats:
- Waterway ecology and other chapters of the River Restoration Manual
- Habitat of rivers and creeks (Water Note 8)
- The management and replacement of large woody debris in Waterways (Water Note 13)
- The importance of large woody debris in sandy bed streams (Water Note 21)
The presence and condition of aquatic habitat is an important indicator of the health of a waterway. It is a major part of the assessment of waterways in the Foreshore condition assessment and the South West Index of River Condition.