Rivers and Streams
Bioregion: All Terrestrial
Relationships with the Landscape
The Natural Capital of Rivers and Streams
Management Themes
Biodiversity Condition
Management Responses
Tables and Charts for Rivers and Streams
Relationships with the Landscape
Freshwater ecosystems are a prominent feature of the landscape in most bioregions. They include a diversity of forms, ranging from permanently flowing rivers and streams, permanent large and small lakes and swamps, through to temporary flowing rivers and streams and small or large temporary wetlands. Biodiversity and conservation considerations for in-stream habitats are discussed here and wetlands (lakes and swamps) are dealt with in the previous section.
There are 3820 named watercourses in Victoria, with a total length of 56 000 kilometres. In addition there are numerous un-named streams, mainly smaller tributaries of named watercourses.
Unlike the relatively discrete terrestrial bioregions already described, there is no clear regionalisation for Victorian rivers and streams. On a simple topographic basis, Victoria can be divided into 29 river basins. However, many of these basins are interconnected, through the Murray River (for north flowing rivers, part of the major Murray-Darling Drainage Division) and, to an extent, through Bass Strait and the historical land bridge to Tasmania (for south flowing rivers, part of the South-East Coast Drainage Division). The differences between the two drainage basins have had major influences on the types and distribution of some of the aquatic flora and fauna, particularly fish, throughout the State.
A single river system can flow through a number of different bioregions. Most of the major river systems in Victoria rise in the high country of the Victorian Alps or the Victorian Midlands, and flow down through the foothills and onto the plains of various bioregions.
For example, the Goulburn River rises in the Alps, descends through the South Eastern Highlands and the Victorian Midlands and finally joins the Murray River in the Riverina.
Across bioregions, there are certain similarities in form (and probably ecological processes) between rivers, depending on the location in the landscape. In a broad sense, these can be divided into mountain, valley and plains segments of rivers. Mountain streams tend to be small, high gradient erosional systems with rocky stream beds and with relatively high flows compared to runoff. Further downslope, as headwater streams join to form the larger valley streams, the gradient is lower and flows are more variable. On the plains, rivers are much larger with low gradients and highly variable flows. While the river changes in width, depth, flow rate and water quality along its length in line with these different landforms, it remains a single linear entity. Its biodiversity characteristics are determined by a complex combination of geography (drainage basin, mountain, valley or plains) and local physical factors (stream size, stream bed form, water, in-stream habitat and riparian quality), floodplain characteristics and management activities, including those both upstream and downstream of any point.
The water, bed and banks of all watercourses in Victoria are deemed to be public land. In 1881, a Crown frontage of between 20 and 60 metres was permanently reserved for public purposes across all water courses in the State, except those areas which had already been alienated. Consequently, the bed and banks of most watercourses in Victoria are deemed to be public land. In many cases, the reserved Crown frontage has been used by the adjacent landowner under licence, and has been subjected to extensive changes in vegetation cover and condition.
It is proposed that the management of these Crown frontages and waterways will be the responsibility of the relevant Catchment Management Authority. Legal entitlements to use of the water are also held by Water Authorities and individual landholders.
Some of the river length is located in national and State parks. Eighteen river segments with special scenic, recreational, cultural or ecological values have been declared Heritage Rivers under the Heritage Rivers Act 1992.
Page Top
The Natural Capital of Rivers and Streams
Rivers and streams support a wide variety of flora and fauna species and communities. Along with two largely aquatic mammals, the Platypus and the Water Rat, there are 38 extant species of essentially freshwater fish (plus one presumed extinct species). Of these, 29 are considered threatened in Victoria.
Within the fish fauna, there is a distinction between species located north and south of the Great Dividing Range. Thirteen species are located only in the Murray Darling Drainage Division while 18 species are found solely south of the Divide. Only six species have distributions on both sides of the Divide.
North of the divide four species are known to be migratory, moving upstream or downstream to spawn at particular times of the year. Murray Cod have recently been discovered to move more than 100 kilometres upstream each year to spawn, before returning to the same section of river. South of the Divide, 13 of the 18 species are known to migrate. Some, such as the Freshwater Herring, move downstream to estuaries to spawn, while others including the Spotted Galaxias spawn upstream with larvae washed downstream to the sea and the juveniles making an upstream migration. The migration behaviour of many of the freshwater fish species is unknown.
The total number of invertebrate species in rivers and streams remains unknown but would far exceed the diversity of the vertebrate fauna. There is much less distinction between north and south of the Divide, but distinct invertebrate faunas have been identified from a number of areas such as streams in the Grampians. There are data to suggest that different macroinvertebrate assemblages exist in alpine, mountain, valley and plain segments. Fourteen insects and 19 crustacean species (including 11 of the 42 known decapod species) have been identified as threatened, although this is likely to be an underestimate of the true conservation status of macroinvertebrates.
Similarly, the biodiversity of plants in rivers and streams has not been adequately evaluated. Larger macrophytes such as reeds are fairly well known, but smaller vascular plants and algae are in need of monitoring and taxonomic research.
Many frogs spend the tadpole phase of their life cycle in streams. As adults, they rely on the moist microclimate in the riparian zones to avoid desiccation, returning to the stream to breed and lay eggs. Many frog populations throughout the world are declining and 10 species are considered endangered in Victoria.
Water birds including ducks, cormorants, spoonbills, ibis, herons and grebes are dependent on aquatic ecosystems for food and breeding. At least 12 species of birds associated with rivers and streams are considered threatened in Victoria. At least one bat species, the Large-footed Myotis, which is rare in Victoria, also depends on rivers for food.
Page Top
Management Themes
Because of the vital nature of freshwater supplies for agriculture, industry and urban living, many factors and issues influence biodiversity outcomes in rivers and streams.
The variable nature of Victorian climate and rainfall lead to a dependence on stored water for agricultural, domestic and industrial purposes. Consequently, many Victorian rivers have been impounded. Extraction of water for domestic or industrial use has reduced overall flows significantly in many places. About 55 per cent of all divertable streamflow is extracted. Large releases of water for irrigation often occur during summer, when natural flows are low. The quality of water released from impoundments is often altered, commonly being far colder than normal. These changes to volume, seasonality and water quality reduce the suitability of rivers and streams for aquatic species. Storage during high flow periods has reduced inundation of the floodplain, which may have been a factor in the reduction of some fish, bird and plant species.
Impoundments create barriers to the migration of fish, restricting the available habitat. Even small structures such as weirs or poorly constructed road crossings, or channelisation, can create barriers to fish movement.
Changing land use has altered the quality of water in rivers and streams. Clearing of native vegetation, particularly in association with irrigation, has led to increased stream salinity, while degradation of stream bank condition through grazing and other activities has increased turbidity levels in some streams. Agricultural practices and domestic and industrial discharges have increased the levels of various toxic chemicals and nutrients in streams.
Many bird, invertebrate and fish species rely on woody debris for resting or breeding. Removing snags for navigation, and during flood and erosion mitigation works, has reduced the habitat quality of many rivers for native fauna. Increased sedimentation that fills either interstices in the stream bed or deep pools also reduces the available habitat in many waterways.
Several species of introduced fish and invertebrates have caused declines in populations of a range of native species. Exotic plants such as willows and blackberries dominate many riparian streamsides. These can change the ecology of rivers and streams, making them less suitable for native biota. Aquatic weeds, including Cord-grass, can also be serious problems where they become abundant.
Page Top
Biodiversity Condition
In 1986, a state-wide survey was conducted of the environmental condition of Victorian rivers and streams. Sites were evaluated for 10 factors likely to be important to aquatic biota, including stream bed condition, bank vegetation, flow, depth and erosion. Results showed that 60 per cent of all streams were classified as being in good or excellent condition, 13 per cent were in moderate condition and 27 per cent were in poor or very poor condition.
The overall state figures included all streams in upland forest areas including national park and State forest.
A high proportion of minor streams were in good or excellent condition (69 per cent), compared with far fewer main streams (21 per cent) and tributaries (36 per cent). The figures for streams in cleared areas were significantly different, with only 5 per cent of streams in good or excellent condition, 30 per cent in moderate condition and 65 per cent in poor or very poor condition.
Stream condition varies throughout the State. Rivers in the east, including the East Gippsland, Tambo, Snowy, Mitchell and Thomson catchments are generally in good condition, with over 90 per cent of the stream length in good or excellent condition. Rivers in the drier west, including the Corangamite, Avoca, Hopkins and Campaspe catchments are in generally poor condition with over 95 per cent of stream length in moderate to very poor condition.
The composition of aquatic macroinvertebrate assemblages in rivers and streams has been used as an indicator of biological health. In general, mountain streams are in better health than valley and plain rivers. Over 90 per cent of mountain stream segments are rated as in excellent or good health based on the macroinvertebrate fauna compared to just over 10 per cent of plains river segments. However, data for 50 per cent of plain segments and 65 per cent of valley streams are insufficient to determine biological health.
Flows below points of water extraction in rivers have been evaluated for their suitability for fish. The diversion of water for domestic purposes has placed moderate to high stress on 104 rivers and streams (67 small streams and 37 larger rivers) during the normal low flow periods in summer or autumn. Only 69 rivers and streams from which water is diverted for domestic purposes release sufficient water to prevent downstream stress during low flow periods.
Of 88 diversions on larger rivers that store water for irrigation, 29 have a significant impact on flows during summer and 59 have flow rates that cause minimum amounts of stress.
The condition of riparian vegetation declines markedly from the upland to the plains segments of rivers. Good quality riparian vegetation, where there is a dominance of native species, width greater than 30 metres and with more than 80 per cent continuous length intact, is uncommon in plains, with 80 per cent of plains segments in poor or degraded condition.
The poor condition of many rivers and streams has resulted in a significant degradation of the native aquatic fauna. Over 65 per cent of Victorian fish species are rated as threatened and 20 of these have been listed under the Flora and Fauna Guarantee Act 1988. Five amphibians are also listed, but fewer aquatic and riparian plants and invertebrates have been listed. Action statements have been prepared for seven of the listed fish, frog and invertebrate species. Ten potentially threatening processes dealing directly with rivers have been listed, but as yet none of these have Action Statements.
Page Top
Management Responses
The low number of streams in good or better condition in cleared agricultural land means that a major improvement effort must be made. Improvements will rely heavily on Catchment Management Authorities, local councils and landowners. The emphasis will be on working with land and water managers to incorporate protection and restoration of rivers and streams into management plans, primarily through the amelioration of threatening processes. It is opportune for strategic actions to be directed towards on-ground works. There is already considerable interest within the community in protecting and restoring rivers and streams, particularly through fencing and revegetating riparian zones. The importance of clean water for domestic, agricultural and environmental use is also well recognised and becoming more important to the community.
Continued research and monitoring will improve our knowledge about the biodiversity of rivers and streams, particularly of plants and invertebrates. It will also identify critical areas for protection and restoration, and assist in determining the appropriate management approaches.
In upland streams, emphasis will be on working with land managers to incorporate protection and restoration of rivers and streams into management plans, through the development and implementation of scientifically-based codes of practice for activities such as roading, timber harvesting and recreation.
The priority management responses for land and water managers and planners are the following:
- Incorporate the approved LCC recommendations for Rivers and Streams into relevant plans and strategies.
- Develop an in-stream and riparian strategy for Victoria, which will help achieve better river management and restoration outcomes, particularly to increase community and landholder custodianship in the rural landscape.
- Ensure that biodiversity information on the in-stream and riparian environments is used effectively in the bulk water entitlements process.
- Promote the adoption of aquatic biodiversity information and conservation management into Regional Forest Agreements, Regional Catchment Management Strategies, and Heritage River, Streamflow, Nutrient and Salinity management plans.
- Promote instream and riparian vegetation protection and restoration as a key environmental outcome for the Natural Heritage Trust program and co-ordinate the strategic restoration of Victorian streams to maximise biodiversity outcomes on the ground.
- Promote the use of fishways over selected barriers with priority given to threatened species and sites that maximise the available upstream habitat.
- Incorporate the importance and benefits of protecting and enhancing native vegetation in the instream and riparian environments in extension and voluntary programs to landholders and the community; these include Land for Wildlife, Farm$mart and Waterwatch.
- Ensure that ‘best practice’ in restoration of riparian vegetation is continually developed and communicated to natural resource managers and landholders and is included in relevant codes of practice.
- In conjunction with other agencies, including the Murray-Darling Basin Commission and adjacent state governments, continue strategic and co-ordinated investigations into the ecology and management of freshwater environments.
Return to 'Directions in Management' content page.