These strappy-leaved plants are growing along the edge of water in Commonwealth Park ponds. I found one with a yellow flower. What sort of plant is it?
Yellow Iris or Yellow flag iris is a showy plant, not an Australian native, and is used as an ornamental in ponds and the like; but unfortunately it spreads readily and establishes downstream, sometimes forming thick stands that are hard-to-eradicate: this is why it is recognised as an 'environmental weed" in some places, like Victoria . You can find Yellow Flag iris in parts of Lake Burley Griffin, downstream of Commonwealth Gardens, such as parts of Acton peninsula, and along Yarramundi Reach. In Yarramundi Reach, I have noticed the numbers are slowly building.