Eradication of aquatic weed in Pāpāmoa now in stage two

The Wairākei Stream site is still marked with tape and warning signs to remind people to keep away. Photo / John Borren

Work to eradicate salvinia – one of the world's worst aquatic weeds – from the Wairākei Stream at Pāpāmoa has entered its second stage.

The Ministry for Primary Industries suspects someone put the salvinia plants into the stream, possibly from their aquarium or pond.

The infestation covered about 1.4km of the stream, which runs behind the housing area.

The site is surrounded by residential properties, sports amenities and public access walkways and parks.

It is marked with tape and warning signs to remind people to keep away.

Salvinia is an unwanted plant and notifiable organism under the Biosecurity Act, meaning it is illegal to grow or share plants.

It can completely blanket waterways, has the potential to destroy the habitat of native plants and animals, and can cause a drowning hazard.

A ministry spokeswoman this week said stage one of the initial removal process was complete.

"Six weeks on we are confident and pleased with the removal process as virtually all the salvinia plants were removed during the initial removal process – even with the extra challenge of flooding in June, over the Queen's Birthday weekend.

"We are very pleased with the results and will add the use of the suction truck and digger to our toolbox for eradicating salvinia."

She said the ministry was now at stage two, which involved regular and frequent checks to remove every last fragment of salvinia from the waterway and banks.

The checks would continue until no further plants were found.

"We must be sure to remove every remaining piece of salvinia because even very small fragments can survive and grow."

The spokeswoman said the ministry would then monitor the stream for a further two to three years to be confident salvinia had been eradicated.

She said as part of Tauranga City Council's general weed management procedure, it had sprayed glyphosate to kill any salvinia plants and any other weeds on the banks and scrub near the stream.

No spray had been used over the water.

Local iwi Ngā Potiki was continuing to work alongside the ministry and the city and regional councils, and was assisting with the regular checks.

The iwi had spent time on site assisting with operations, monitoring for eels during the suctioning, and ensuring appropriate cultural processes were respected.

If you have salvinia on your property call the MPI pest and disease hotline 0800 80 88 66 and MPI will arrange for the plants to be disposed of in a safe manner.

Salvinia molesta (salvinia)
• Is known worldwide for its fast spread and significant impacts on lakes and waterways.
• Forms dense mats on the water surface and has the potential to destroy the habitat of native plants and animals, including native aquatic birdlife.
• Attracts breeding mosquitoes, removes oxygen from the water, affects recreational activities and creates a drowning risk for people and animals.