The Marlborough District has over 12,000 kilometres of freshwater streams and rivers, ranging from large rivers such as the Wairau and Pelorus, to the small forest streams of the Marlborough Sounds.
Surface water is important for the social, cultural and economic wellbeing of the district. Surface water is used for a variety of purposes including domestic takes, agricultural, industrial and irrigation. The demand for these uses must be balanced against what is required to maintain the ecological wellbeing of waterways and protect in-stream values.
The consumptive use of surface water resources can place pressure on the ecological wellbeing of waterways. Rivers support a range of in-stream values that are largely sustained by a sufficient quantity of water and a particular flow regime. Lowered water levels can reduce the area of habitat available for fish species and stream invertebrates.
The overall health of the waterways is determined by land use in the surrounding area and overall catchment. The land use around the stream and the land use in the catchment are both very important influences on the overall health of the waterway. The land use strongly affects the types and varieties of stream habitat and the amount of riparian vegetation growing along the stream banks.
The riparian vegetation (the plants that grow along the stream banks) provides shade and also influences the water level in the stream as well as the degree of flooding and stream bank erosion. The riparian vegetation also provides spawning habitats for galaxias species. Leaves and other organic matter that wash into the stream provide an important food source for the organisms living in the stream. Larger pieces of woody debris in the stream provide a variety of habitats to suit different organisms.
The Marlborough region includes a variety of freshwater environments including wetlands, rivers and streams. The main river catchments include the Awatere, the Wairau and the Pelorus.
Numerous other smaller waterways and streams are also present, especially in the Marlborough Sounds, and some of these are still in a very natural state and provide habitat for a good range of native fish, including species like the banded and shortjaw kokopu, red-finned bully and long-fin eels.
A feature of the drier south Marlborough area is the presence of many ephemeral waterways - those that are seasonally dry for part of the year.
Overall about 19 species of native fish are found in Marlborough's waterways (there are 35 species found in New Zealand overall) the most common being inanga, common bully and eels. Other introduced species like trout and salmon, are also found in some local rivers.
Aquatic macroinvertebrates (small animals with no backbone, that can be seen by the human eye) are also an important part of the freshwater ecosystem. They are an important source of food for fish and also feed on plant and algae material within the system.