Native freshwater fish populations are affected by obstructions to fish passage because their natural movements throughout river systems are compromised. Artificial barriers such as dams, weirs, causeways and culverts obstruct the free passage of native fish by preventing or impeding their movement from one part of a stream to another. All freshwater fish need to move between habitat areas at some stage in their life cycle to spawn or seek food and shelter, with many having definite migration requirements. Therefore, obstructions which impede the free passage of fish often result in declining populations or local extinction.

A survey was made to identify and document fish passage obstructions in the coastal rivers of south-eastern New South Wales. The area studies ranged from the Wollongong Coast south of Sydney to the Victorian border, also including the Snowy River. This area comprised a total of nine of the Australian Water Resources Council Drainage Basins, including the Wollongong Coast (No. 214), Shoalhaven River (no. 215), Clyde River-Jervis Bay (No. 216), Moruya River No. 217), Tuross River (no. 218), Bega River (No. 219), Towamba River (No. 220), East Gippsland (No. 221) and Snowy River (No. 222).

A total of 254 obstructions were documented, comprising high dams, farm dams, fixed crest-weirs, rock weirs, stream-gauging weirs, culverts, causeways, bridges and tidal floodgates. Overall, causeways and culverts were the most common structures found to obstruct fish passage. The largest number of obstructions occurred in the Shoalhaven River Basin, where a total of 90 artificial barriers were present. A total of 47 obstructions occurred in the Wollongong Coast Basin, 25 in the Clyde River-Jervis Bay Basin, 24 in the Snowy River Basin, 24 in the Bega River Basin, 18 in the Tuross River Basin, 17 in the Towamba River Basin, 6 in the Gippsland River Basin, and 3 in the Moruya River Basin.

A "fishway priority scheme" was developed to provide a quantative, objective basis to rank the priority of a fish-passage restoration project for any obstruction, either by building a fishway or removing the obstruction. Eleven criteria were used, including details of the size of the river system, location of the obstruction, presence of threatened species, severity of the obstruction and other relevant features.

The Fisheries Management Act (1994) has various provisions for maintaining fish passage in streams, these are summarised in the publication: "Policy and Guidelines. Aquatic Habitat Management and Conservation 1998". The current survey has shown that there are numerous obstructions to fish passage which impede migration and threaten biodiversity in many south coast streams. Fish passage needs to be restored as a major step in restoring healthy rivers.

Aims and objectives

It as noted by Harris (1984a) that only limited information was available about the occurrence and features of physical barriers in Australian streams. Until recently there has also been little control over the construction of these barriers. In the Shoalhaven catchment below Tallowa Dam, only 11 structures were found by Harris (1984). In 1995, however, Timms found 62 barriers for the same area. However, Harris’s study was on a broader scale, and only weirs and dams on streams were surveyed (e.g. low-level weirs, causeways, culverts and floodgates) as well as dams and weirs. These small-scale obstructions may still cause serious problems for fish passage. Because Harris’s 1984 study was completed over a decade ago, and did not include small-scale obstructions the need for a more up-to-date inventory of barriers to fish passage on the streams of the south coast of NSW was identified.

The main aims of the project were:

• to locate, identify and document the barriers to fish passage which occur on NSW south coast streams.
• to estimate the amount of fish habitat being obstructed,
• to prioritise the barriers found in terms of the need to provide for fish passage at these sites, and
• to prepare a strategic plan of future actions to address the problems posed by these barriers.