Know The Enemy: Water Hyacinth

The Water Hyacinth is a native of South America and could be very destructive to our lakes, rivers and waterways. Our country has been clear of the plant for at least twenty years. But we still need to be on the lookout - the seed of Water Hyacinth may remain viable for up to twenty years and in New Zealand it has been found at a site that was clear for seven years.

Water Hyacinth is mostly found in warm areas like Northland and Auckland, and as far south as Wellington. Each plant has a free-floating rosette of shiny, rounded leaves and a thick mass of feathery roots hanging in the water. The roots are often dark in colour and can reach 2.5 m in length. A single flowering stalk up to 50 cm above the leaf canopy is produced from the rosette. At the top of the stalk is a cluster of 5-15 mauve-blue flowers.

Each plant consists of a free floating rosette of shiny, rounded leaves and a thick mass of feathery roots hanging in the water. The roots are often dark in colour and can reach 2.5 m in length. A single flowering stalk up to 50 cm above the leaf canopy is produced from the rosette. A cluster of 5-15 mauve-blue flowers tops it.

Each plant can produce 3-4 daughter plants at the end of its stolons, which in turn produce further plants that can form a dense mat, which can break up and move to new areas. The negative effects of mats of water hyacinth are similar to those of salvinia.
Biosecurity NZ has a monitoring and control programme to keep Water Hyacinth out of New Zealand, but we need your help. Please know what it looks like and keep watch for it. In the past, New Zealanders have made major pest discoveries in their backyards and neighbourhoods.

The seed of water hyacinth may remain viable for up to twenty years and in New Zealand plants have been found at a site previously clear for seven years. Long term programmes are required to prevent re-infestation of sites.

If you find Water Hyacinth, please call Biosecurity New Zealand on 0800 80 99 66.

For more information on this pest or others, visit the Biosecurity New Zealand website.