Giant reed recorded at two Swan River locations this year

July 29, 2026

(Arundo donax) has been observed at two separate locations along the Swan River this year — a fresh sighting on the Mounts Bay Road foreshore three days ago, and two earlier records from Maylands in April. At five metres tall and spreading aggressively by rhizome fragments carried downstream in winter flows, this is one of the world's most destructive riparian invaders.

The timing of winter sighting is important: fragments travel farthest in high flows, and the weed stays conspicuously green while native understorey dies back, making this the best season to locate it. The same riverbank habitat holds , a native tree that iNaturalist flags as threatened, recorded three times this month alone. Giant reed is known to alter soil chemistry and hydrology in ways that make riparian recovery difficult even after removal — a concern worth keeping in mind given the co-occurrence of both species within the same stretch of riverbank, and one that underscores why early detection matters here.

Data from iNaturalist

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