Waterhen Lake was breathed into life in the 1970s. The lake’s primary purpose was to be used only as a stormwater retention basin for the collection of runoff from the surrounding hills, the settling of sediment, then outflow into the Coomera River. Over time, of course, the hills are now suburbs and runoff includes garden fertilisers, grey water and road accretions.
The lake has an average depth of around 400mm, with some deeper sections of 1.6metres due to the island wildlife refuge having been excavated from the bed of the lake. Over time the entire lake and island have become increasingly used by breeding birds (primarily ibis which are native to Australia, egrets of all four species – cattle, little, intermediate, and great eastern – little cormorants, and a pair of black swan). There is some justification for an argument to increase the size of the island refuge however that may only encourage more ibis to breed which is not on the City of Gold Coast’s agenda. Additionally the resident waterbirds (purple swamp hen, Eurasian coots, dusky moorhen, ducks…..) also use the island for breeding purposes, though not so readily observed. There is also a significant population of feral geese and ducks, along with seasonal visitors such as curlews, whimbrels, stilts, dotterels, spoonbills and many others. This proliferation of bird life produces significant pollution in the waters of the lake.
One species of bird which has significantly increased in numbers over recent years is the native magpie goose; this bird commenced occupation on the coast some 6 or so years ago is often present in significant numbers (over 100 individuals) which causes a taxing of the lake and its ecology. For example, what was a developing mudflat at the western inflow is now just a mushy swamp due to the perpetual foraging of both magpie geese and ibis, but mainly magpie geese as there was no problem prior to the influx of magpie geese; areas we have planted out along the bank where magpie geese congregate has seen the decimation of plants in those areas with the constant need to re-plant. It is believed drought has caused the magpie geese to remain in such large numbers, as well as the birds reclaiming what was apparently part of their original range. Magpie geese were hunted for many years for their meat.
Water quality is one aspect which has not improved over time, primarily due to the increased use of the island refuge as an almost continuous breeding space.
The Coomera River Catchment Care Group (CRCCG) monitors water quality monthly and the principal factor affecting water quality are the ammonia and nitrates produced by bird waste; interestingly, the phosphates from grey water are at a relatively normal level most of the time. The high readings of ammonia and nitrates has one surprising side effect and that is the proliferation of the native firetail gudgeon in sufficient numbers to feed up to a dozen pelicans and some 70 small cormorants from time to time. Other life in the lake consists of short finned eels, Brisbane River turtles in good numbers, and some carp of large proportions. Council has introduced some 2000 freshwater mussels in an effort to test how best to improve water quality.
Unfortunately the island vegetation is almost exclusively weed species and the City of Gold Coast is currently planning to replace the weed species with native species which are also valued as nesting trees and shrubs. This will be undertaken in three stages so as to cause least disturbance to breeding birds. Similarly the banks of the lake are mostly stabilised through the growth of feral trees such as the Indian coral tree; it is planned to replace these through judicious plantings over time, as was done recently in the south eastern inflow area.
Erosion is a constant in some areas as the shallow waters allow prevailing winds to slowly wear the bank down. The observed current rate of erosion in some areas is as great as 100mm per annum. Future plantings will assist in curtailing the effects of this erosion, although additional remedial measures (such as placement of bulrushes or stone on the edges) may be necessary.
Soil quality does vary significantly and in some areas retards our best efforts; on the eastern shore the soil is hydrophobic to the extent that plantings of two years will still require watering in a dry period, such as the summer we have just endured. This soil also inhibits what can be planted and shrubs and trees cannot survive dry weather and water repellent soil.
The CRCG, working with the City’s Catchment Management Unit (CMU) has been planting along the lake for the past three years. Good results have been enjoyed on the western end, however the northern side and eastern end have required a lot of work to have made a difference. Our grasses (lomandras) are sourced through Nerang Riverkeepers at Country Paradise Parklands in Nerang where we regularly go to pot up the grasses to 140mm size, whilst the shrubs and trees are sourced by CMU.
Future plantings will include more shrubs and trees as we attempt to provide greater cover for smaller birds, lizards and also shade for the native water fowl. We are hoping that in time we will produce sufficient cover for frogs to re-establish themselves, as they were decimated by the influx of feeding birds such as white faced herons and spoonbills.
The CRCCG aims to make a difference in every way that we can, in partnership with as many willing local people as we can find, for the betterment of our community and its environment.
For more information please contact Steven Gill 0400 617 000
This article was produced for the 5th Gold Coast Catchment Crawl, 13th April, 2016