Description of Carex maculata fits the plant at this site pretty well, but the climatic range does not. The natural distribution of Carex maculata is coastal NSW, north of Sydney and PlantNet even uses the word “rainforest”: this implies a very different temperature range from that experienced in the dam at this site where the plant now occurs, which includes being frozen. For me, climate for Cx maculata in its natural range makes it unlikely that this plant is Carex maculata - but not impossible! It’s a puzzle
As a temporary measure, I have confirmed this as Carex ( even tough we are unable to resolve to species) to save it from appearing to be Lomandra longifolia, which it certainly is not.