A joint Biosecurity New Zealand and Waikato Regional Council work programme is underway following the discovery of a small cluster of the pest water hyacinth in the Waikato River near Huntly.
The agencies are working together with local iwi to ensure any water hyacinth present is located and safely removed. The team will then coordinate ongoing checks to make sure it hasn't come back.
Biosecurity New Zealand's manager of pest management, John Sanson, says water hyacinth is a rapidly growing water weed that if left, can form dense mats that reduce water quality, crowd out native water plants and animals, block irrigation systems and alter ecosystems.
"In this instance, we've found just 2 individual plants in the slow waters at the edges of the river and 1 plant in a cluster of willows further out into the stream.
"The plants have clearly come from a container of water hyacinth being kept at a private property in Huntly backing onto the river. This container was close to a drain next to the river bank and we believe that's how the plants entered the waterway."
Mr Sanson says all known plants have been removed from the water and inspections have found no further sign of the weed.
However, as a precaution, a more comprehensive survey is taking place today, (4 March) using a boat supplied by the council harbour master.
"Two biosecurity inspectors are carrying out the search, accompanied by a person from the Waikato Regional Council and a representative of Waikato-Tainui.
"The team is systematically checking the banks downstream of the site for 15 kilometres, paying attention to stands of willows and backwaters where plants could be harboured. The survey is expected to take all day."
John Sanson says if any water hyacinth plants are found, they will be removed under quarantine for destruction and the site GPS-marked. Following the survey tomorrow, the area will be regularly surveyed for 20 years to make sure the plant doesn't come back, as water hyacinth seeds can survive for a very long time.
"This is a pest weed that is taken very seriously. It is one of the pests being eradicated under the National Interest Pest Response programme led by Biosecurity New Zealand in partnership with regional councils.
"It is illegal to sell, propagate or distribute this plant. If people believe they've seen it, please contact our pests and diseases hotline 0800 80 99 66."
Water hyacinth fact sheet [PDF, 1 MB]