Glenbrook Lagoon

Glenbrook Lagoon is a heritage-listed site located in the suburb of Glenbrook in the Blue Mountains 10 kilometres west of Penrith and 3.8 km from Nepean river. The lagoon is a natural flat-bottom freshwater lagoon with an average depth of 2.7 metres and a maximum depth of 4.05 metres. The lagoon covers an area of 7 hectares. It relies on waterflow from the surrounding area. The lagoon is also fed by natural springs. Glenbrook Lagoon is one of only three lagoons of this kind in the Hawkesbury area water catchment. The lagoon and its surrounding area provide an important natural sanctuary for native flora and fauna. Currently the lagoon is used as a nature reserve and tourist attraction. Glenbrook Lagoon is of great cultural and historical significance to the people of the Blue Mountains. ==History==

Bordered by residential areas on four sides, Glenbrook Lagoon serves as a reminder of the area's historic bush past. Best known for being found by William Lawson, William Wentworth and Gregory Blaxland on their crossing of the Blue Mountains in 1813; Blaxland, In his journal, described the way he "fell into a large lagoon of good water of very coarse rushes". == Ellis family cottage ==

The Ellis family lived in the area in the 1940s, running an orchard and garden, in spite of the poor-quality soil. The land was clear at the time, but has now returned to nature after work carried out by the Glenbrook Lagoon Society Bushcare group, Blue Mountains City Council and the Urban Runoff Control Program. The remains of the Ellis family cottage are located a hundred metres north of the lagoon. ==Uses==

The lagoon was first used as a military depot. The depot was used to check the permits of travellers who were planning on traveling over the Blue mountains. The lagoon was then used throughout 1867 to 1913 as an essential part of the Zig Zag railway system which took passengers through the Blue mountains. Pipes took lagoon water to Glenbrook railway station providing the railway system with an important source of water. As a result, the left side (Eastern side) of the lagoon was dammed in order to make the lagoon bigger and a larger source of water for the railway. The dam wall is currently used a road that allows residents to pass the lagoon. This road is currently known as Glenbrook road but was previously named Railway street. In the 1860s the lagoon was also used as a dam to provide drinking water for the people living in the small town of Glenbrook The lagoon is currently used as a historical tourist attraction and bush walking site. The lagoon and its surrounding area also provide an important natural sanctuary for native flora and fauna which is quite unique in the urbanised township of Glenbrook. Glenbrook lagoon also plays an important role in fighting bushfires. Helicopters use large buckets to collect the lagoon water and dump it over out of control bushfires. The lagoon water has been used in this way for several bush fires in 2001, 2013 and 2017. == Significance of the Lagoon ==

Due to its rich historical value the lagoon is holds great cultural significance to the local area. The lagoon was also previously used as a place to swim and fish by the local people. Therefore, it holds many fond memories for the people of Glenbrook. Due to the role in which the lagoon has played throughout the history of the Blue mountains especially in regards to its uses with the Zig Zag railway it has been deemed that Glenbrook Lagoon Carries a great historical significance for the people of the Blue mountains. The lagoon also hosts a range of native species of flora and fauna. The lagoons surrounding area features large Euclaypt and Angophora Costa (Eucalyptus piperita) trees, which are unique to the location of the lagoon. These trees provide a suitable habitat for the Peron's tree frog (L. peronii). The dense rushes such as Grey rush (Lepironia articulate), Spike rush (Eleocharis sphacelata) as well as fallen logs surrounding the edges of the lagoon, make good foraging habitat for native wetland birds such as the Swamp hen (Genus porphyria). These native plants also provide some protection from predators allowing for possible breeding spots. The rushes also provide habitats for frogs including the Striped Marsh Frog (Limnodynastes peroni) and the Eastern Dwarf Tree Frog (Vitoria fallax). The lagoons surface is also populated with native Bladderwort (Utricularia australias).The Bladderwort also provides foraging habitat on the lagoons surface. It is these native species which the surrounding area of the lagoon and its surrounding areas play host to that give the area its aesthetic significance. == Pollution of the Lagoon ==

The damming of the left side (Eastern side) of the lagoon for the zig zag railway has caused issues for the lagoon mainly because it caused the lagoon to become a closed water system and any pollutants are unable to be flushed out of the lagoon naturally. In turn this has led to a significant buildup of pollutants carried by storm water into the lagoon. Without proper drainage of this water, significant environmental issues have risen including the growth of noxious weeds which have effectively choked out natural aquatic flora and fauna living in the lagoon. Cabomba has been listed as a class 5 noxious weed and also as a weed of significance and had been notably difficult to remove in past situations. Both of the noxious weeds (Cabomba and Salvina) cause severe oxygen depletion in the lagoon as they die and decompose using most of the dissolved oxygen available in the lagoon. This makes survival difficult for other aquatic organisms including native water plants, native fish and turtles. == Treatment of Cabomba and Salvina Weeds ==

The presence of The Cabomba and Salvina weeds in the lagoon posed a serious threat to native flora and fauna and also introduced the threat of the noxious weeds spreading into nearby waterways such as the Nepean river, Hawkesbury river and the many waterways within Blue Mountains National Park including catchments which lead to Warragamba Dam. The Dam is a major waterway which provides much of Western Sydney's drinking water. In order to combat this threat during 2006 a $95 000 grant was given to the Blue mountains city council to commence work on re-generating the lagoon and removing the noxious weed Salvina. Regeneration efforts involved the mechanical harvesting of 200 tonnes of Salvina and also the use of herbicide spot treatment with some hand removal of the remaining weeds. However up until 2012, 100 percent of the Lagoons water column was still filled with the noxious Cabomba weed. In 2012 the Blue Mountains city council was given another grant to remove the Cabomba weed. Removal of the Cabomba weed in December 2012 included the use of the herbicide Carfentrazone-ethyl which was intended only to kill off 50% of the Cabomba weed growth in the lagoon. However the herbicide successfully killed off the Cabomba weed entirely from the water body. The removal was considered a success however during this treatment some native fish mortalities occurred due to oxygen depletion levels this caused levels of fish species living within the lagoon to diminish. These declining oxygen levels where attributed to the large amounts of breakdown of the dead Cabomba weed matter caused by the use of the herbicide. To combat these declining dissolved oxygen levels Generators and pumps were brought to the lagoon attempt to re-oxygenate the water. However these efforts produced limited results the task of re-oxygenating the lagoon proving to difficult with the little power supply to run the generators and pumps and noise complaints from local residents. A water quality monitoring program was also set up at the time these attempts to kill off the weed were implemented. The hopes of this program were that it would be able to successfully monitor water quality, biodiversity and weed control outcomes of the lagoon. This was the first removal of the Cabomba weed on a large scale area in New South Wales using the chemical Carfentrazone-ethyl. Bush-care groups continue regeneration work on the lagoon and its surrounding areas in hopes of restoring the natural environment to provide habitats for the native fauna and flora. These Bush-care groups also encourage the use of native aquarium plants instead of exotic and noxious ones such as Cabomba, as it is believed that the dumping of these noxious weeds caused there significant growth and presence within the lagoon. == Current State of the Lagoon ==

Regeneration efforts at Glenbrook lagoon have resulted in a 99% decrease of the noxious weed Salvina. The program also plans to regularly monitor the water pollution levels in the lagoon. It is hoped that through these efforts the lagoon will remain as a healthy eco-system and will continue to be a sustainable habitat for native flora and fauna. ==References==