‘River connectivity’ is the degree to which waterways and waterbodies are linked across a landscape. In some cases connectivity may be almost continuous such as a main stem river, or discontinuous such as ephemeral tributaries or billabongs that are recharged during times of flood.

Many native fish using inland waterways migrate to different habitat at key stages in their life cycle, such as to breed, avoid predators and competitors, and to find feeding grounds. It is vital to ensure fish have access to these different habitat areas.

Unlike Northern hemisphere fish such as trout and salmon, our fish are not strong or very agile swimmers. T hey are often unable to negotiate obstacles such as small waterfalls (as little as a 10 cm drop) or The construction of dams, weirs and regulating structures, poorly designed road crossings and block banks across floodplains have reduced connectivity and prevented fish from accessing essential breeding and feeding habitat.

These structures also affect the downstream movement of native fish, with adult fish actively avoiding going over weirs. Mortality levels are higher in drifting fish larvae that pass through undershot weirs, which release water beneath a series of gates.

Over 4,000 licensed barriers have been identified in the Murray-Darling Basin. T his figure is likely to be considerably higher when privately owned structures, which are yet to be identified, are considered. T he collective impact on native fish through restriction to habitat is considerable.

These structures may also bring changes to natural flow regimes. Changes such as reduced downstream flows, reduction in frequency or volume of bank topping flows that connect billabongs and wetlands, or a variation in the time of year when flows are released, can all affect the breeding and feeding opportunities of native fish..

MANAGEMENT OPTIONS

• Maintain and improve river connectivity

MANAGEMENT ACTIONS

• Seek advice to see if existing structures are fish friendly
• Remove structures that are no longer required
• Make existing structures fish friendly using fishways on weirs and culverts through block banks and causeways
• For any new structures ensure passage is provided for fish.Options can include: box culverts and pipes through crossings and block banks, bridges or arch structures and fishways or fish ladders on weirs.

REMEMBER
Permits are required for works that are conducted instream. Advice about fish-friendly structures and legislation requirements can be obtained from I&I NSW (Fisheries).