The installation and operation of in-stream structures and other processes that alter natural flow regimes is a listed Key Threatening Process under the Fisheries Management Act 1994 and the Threatened Species Conservation Act 1995 (DPI, 2006). Recommendations put forward by the acts specifically note the impact of in-stream structures on the life histories of threatened freshwater fish species including Silver Perch, Macquarie Perch, Purple spotted Gudgeon, Olive Perchlet, Murray Hardyhead, Southern Pygmy Perch, Murray Cod and Trout Cod.
In 2006 after an extensive state-wide review, 16 structures within the Lachlan river system as listed in the table below were prioritised and appropriate remediation actions recommended in the NSW DPI’s (2006a) “Reducing the Impact of Weirs on Aquatic Habitat– New South Wales Detailed Weir Review: Lachlan CMA region“. This detailed weir report for the Lachlan provide comprehensive accounts of the structures operational details, system hydrology, ecological considerations, proposed remediation options (along with projected costs), and preferred NSW DPI option for improving fish passage at the weir. A complete data set for each weir is stored in the NSW Department of Primary Industries Fish Habitat Database.
As of November 2011, native fish fishways or fish ladders, and fish counters were installed at Lake Cargelligo, Island Creek, Bumbuggan Creek and Booligal weirs as part of the Fish Superhighways Program: opening up a total of 284 kms of waterway (State Water Corporation, 2014). The Fish Superhighways Program aims to readdress the historical legacy of restricted fish passage by facilitating migration, which native fish depend on to breed, seek refuge (e.g. from drought) and disperse into new habitats.
In addition to the 16 weirs prioritised by the NSW Detailed Weir Review, the following structures are relevant to water planning and operational delivery in the Lachlan:
- Lake Cargelligo Weir, and inlet and outlet channels and regulators: a map and description of these features can be viewed and read in an internal Lachlan Riverine Working Group (LRWG) draft document titled ‘Lake Cargelligo: post regulation history‘. Another key reference for Lake Cargelligo as a storage is Thurtell et al., 2003 ‘Lachlan Lower Lakes Water Quality Investigation‘.