Blue Mountains City Council

Glenbrook Lagoon

Glenbrook Lagoon is a rare upland wetland that is one of only three of its kind in the entire Hawkesbury-Nepean System. The Lagoon provides habitat for flora and fauna species that are otherwise unusual in the area, however the ecosystem values of the lagoon are degraded by the level of urbanisation in the catchment. For many years, large amounts of sediments and nutrients have flowed into Glenbrook Lagoon from the surrounding residential areas. This has encouraged the growth of nuisance aquatic plants, which 'choke' the lagoon and make it unsuitable for the native aquatic plants and animals that would normally live there if conditions were better.

Two noxious aquatic weeds are of major concern at Glenbrook Lagoon; they are Cabomba caroliniana and Salvinia molesta.

Glenbrook Lagoon Restoration Project

Blue Mountains City Council has an ongoing commitment to restore the ecological condition of Glenbrook Lagoon. Since 2006, Environment Levy and external grants have been used to control aquatic weeds, improve water quality, conduct bush regeneration works and engage the local community at the lagoon.  Prior to this a range of other works were undertaken at the lagoon, including the construction of three stormwater detention basins in the mid-1990s as part of the Urban Runoff Control Program, bush regeneration works and Salvinia weed control.

Cabomba control at Glenbrook Lagoon

Cabomba caroliniana is a noxious aquatic weed listed as a Weed of National Significance in Australia. Since the early 1990’s Cabomba has infested Glenbrook Lagoon and in 2012 was covering close to 100% of the lagoon area. A viable method of controlling Cabomba became available in August 2011, when a herbicide was registered for the control of Cabomba in closed waterbodies in Australia.

In December 2012, the herbicide was applied, achieving complete control of Cabomba across the entire lagoon. Follow-up monitoring including surface visual observations, benthic grabs, underwater video, and diver surveys did not find any evidence of Cabomba regrowth until January 2017.

Four years after herbicide treatment, Cabomba was found regrowing in the lagoon. Regrowth ranged from small, dense patches close to the surface to sparse patches or individual plants growing in deep water (2 – 4 metres).

A Secondary Cabomba weed control program was commenced in 2017 and will continue until 2020 and beyond. For more information please download the 2017 Glenbrook Lagoon Cabomba Report and Management Plan (available at the right hand side of this page).
 

Salvinia control at Glenbrook Lagoon

In 2006 and 2007 Council secured a total of $95,000 from the Local Government Advisory Group of the Hawkesbury-Nepean Catchment Management Authority to undertake project works at Glenbrook Lagoon. Actions included the mechanical harvesting of 200 tonnes of Salvinia in 2006, spot-spraying with herbicide and ongoing hand picking of remnants on a regular basis during 2007-2012.

As a result of the above activities a 99% reduction in Salvinia coverage has been achieved as of June 2012. Ongoing monitoring and maintenance of Salvinia control will be crucial to the long-term suppression of the weed at Glenbrook Lagoon.

 

7th Australian Stream Management Conference - Full Paper

"Factors influencing deoxygenation following an unintended whole of water body herbicide treatment of aquatic weed cabomba in a natural wetland in the Blue Mountains, NSW, Australia." - this paper can be downloaded from the righthand side of this page.

 

19th Australasian Weeds Conference – Full Paper

"Managing a priority outlier infestation of Cabomba caroliniana in a natural wetland in the Blue Mountains, NSW, Australia – could this be eradication? " - this paper can be downloaded from the righthand side of this page.

Glenbrook Lagoon fish surveys

Fish surveys conducted in 2014 found populations of four native fish species at the lagoon (Freshwater Catfish, Australian Smelt, Flat-headed Gudgeon and Long-finned Eel), along with one noxious fish species, Eastern Gambusia. Two native turtle species were also recorded: the Eastern Long-necked Turtle and the Sydney Basin Turtle. For more information please download the Fish Surveys at Glenbrook Lagoon report, to the right of this page. 

 

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