These sightings are evidence of rapid colonisation of the new stormwater treatment wetlands by Gambusia holbrooki – first noticed there on 29 March 2020. (Photo of captive specimen by Bron King).
The arrival of G holbrooki in less than a year after the commissioning of the wetlands illustrates its invasive potential.. The mode of its arrival is unclear. A possible route is via the wetland bypass drain which, when in flood, forms a continuous flow between the wetland intake and Ginninderra Creek (a distance of 180m). Supporting evidence is the continuing presence of G holbrooki in the bypass drain, 130m upstream from the creek. Contrary evidence is that G holbrooki has been seen only in wetland Pond 2. If it entered via the wetland intake, it would be expected also to colonise Pond 1, the settlement pond.
A plausible alternative is that G holbrooki was accidentally introduced to Pond 2 in water brought onto the site in tankers at the time of commissioning the wetlands.