Aquatic

Myall Lakes is one of the largest coastal lake systems in New South Wales boasting over ten
thousand hectares of waterways set wholly within the Myall Lakes National Park. The Myall
Lakes system comprises a series of lakes including the Bombah Broadwater (lower lake),
Two Mile and Boolambayte Lakes (mid-lakes) and Myall Lake (upper lake). Feeding this lake
system is a catchment area of 78,000 hectares. The Myall and Crawford rivers are the main
tributaries to the lake system, feeding into Bombah Broadwater, while Boolambayte Creek
also supplies fresh water. The Lower Myall River connects this unique waterbody to the
ocean, allowing saltwater exchange from Port Stephens. Myall Lakes has significant
environmental and cultural value to the local, national and international community. The lake
system is recognised internationally under the Ramsar Convention as an important wetland,
and Myall Lakes National Park is a popular tourist destination for camping, bushwalking,
fishing, boating and water sports. A healthy lake system is integral to the culture and
economy of the local area.
In early 1999 Myall Lakes began to exhibit major signs of a natural system in trouble when a
large, toxic blue-green algae bloom formed in the lower section of the lakes. Blue-green algae
are a type of bacteria that act like plants by using light for photosynthesis. When conditions
are ideal they can multiply at a prolific rate resulting in a bloom. Potentially harmful algal
scums accumulated on the shores of the lake including at many popular camping areas. The
bloom persisted on-and-off until April 2001 having a major impact on the local community –
tourist numbers dropped and the lakes were intermittently closed to commercial and
recreational fishing. Blue-green algal blooms have continued to occur in the lakes since mid
2001, although not as severely as those experienced in 1999.
The initial algal bloom in 1999 left the Myall Lakes community extremely concerned about
the future of their unique natural asset. The State Government responded to these concerns by
initiating the ‘Monitoring Blue-Green Algae in Myall Lakes’ project - a partnership between
the then Department of Land and Water Conservation (DLWC; now Department of
Infrastructure, Planning, and Natural Resources [DIPNR]) and the NSW National Parks and
Wildlife Service (NPWS: now part of the Department of Environment and Conservation
[DEC]) with funding from the Federal Government’s Coasts and Clean Seas program.

As one of the component policies of the New South Wales State Rivers and Estuaries Policy, the Wetlands Management Policy provides guidance on wise use, best management practice and rehabilitation of wetlands. By adopting the policy, the State Government will give explicit consideration to the biophysical requirements of wetlands to ensure their sustainable management. Principles to be followed include formal recognition in water allocation and management plans of environmental water regimes for wetlands, encouragement of land uses that maintain wetland habitats and processes, discouragement of purpose built wetlands on the site of viable natural ones and the active rehabilitation of degraded wetlands and their habitats. Implementation of the policy will require application to Government agency's activities, coordination of the wetland work of Government agencies, provision of support to the community and preparation of an annual Wetland Action Plan (A).

This paper reviews studies of relationships between riverine fish and woody debris at micro andmeso-habitat scales, and discusses the potential functions of instream structure for lowland river fish.

Experimental research, mainly in North America, has identified three main functions of woody debris as microhabitat for fish in upland streams: overhead cover that decreases predation risk both vertically and horizontally; horizontal visual isolation that reduces contact between fish; and velocity refuge which minimizes energetic costs. As with habitat features in other aquatic environments, increasing spatial complexity of woody debris may modify predator–prey interactions and provide greater surface areas for the growth of prey items. Woody debris may also provide spatial reference points for riverine fish to assist them in orienting within their surroundings. Lowland rivers differ from upland streams in terms of a number of physical variables, including turbidity, depth and water turbulence. Relationships between fish and woody debris in lowland rivers are likely to rely on mechanisms different to those in upland streams.

Recent initiatives involving the reintroduction of woody debris into previously cleared lowland rivers toeplace lost fish habitat are a positive development for lowland river restoration. However, if woody debris reintroduction is to maximally benefit lowland river fisheries, there is a requirement for better understanding of the ecological functions of woody debris in lowland rivers.

Understanding the flux of organic carbon in streams and rivers is essential to the sustainable management of riverine environments as healthy and natural ecosystems. This is particularly important because human activities result in considerable changes to the global carbon cycle. The sources of organic carbon for aquatic food webs are discussed, with a particular focus on the effects of riparian clearing on natural balances and ecosystem function (A).