South East Regional Centre for Urban Landcare (SERCUL) and the Wilson Wetland Action Group received funding from the State Natural Resource Management program to stop the weed from spreading.
SERCUL Canning River restoration officer Matt Grimbly said hydrocotyle, commonly known as floating pennywort, was dangerous because of its rapid growth rate. Mr Grimbly said hydrocotyle had been in the river since the 1980s and caused a major problem in the summer of 1992.
‘Back in the ’90s there was a period where it completely covered the Canning River upstream of the Kent Street Weir for 3km,’ he said.
‘Hydrocotyle can double its biomass in three days to a week, so it can cause big problems if unchecked.
‘The main issue is that it can grow right across a water body, resulting in low oxygen level in the water and blocking out sunlight.’
A Swan River Trust report estimated the mass of weeds weighed 2000 tonnes and cost $1.2 million to eradicate.
‘My guess is that with a bit of luck we could hopefully have it gone from the Canning River in three years,’ he said.
Mr Grimbly said the weed was native to South America and likely got into the Canning River through the aquarium and water-plant trade.
‘It tends to build up in slow-moving or still water and forms dense, floating mats,’ he said.
‘Not only is it a problem for native plants and animals, but it can be dangerous for people who think it is a solid surface and fall into the river.
‘It also stops people from kayaking and canoeing in the river.’
Mr Grimbly said action was required monthly to keep hydrocotyle under control.
He said it was also the responsibility of land managers to prevent the weed from spreading in their own areas.
SERCUL also collaborated with the Water Corporation to control hydrocotyle infestations of drains in Cannington, Wilson, Waterford and Welshpool.