News and stories

Salvinia eradication at Wairakei Stream


17 October 2018

After just one phase of eradication of Salvinia (Salvinia molesta), Wairakei Stream in Papamoa is looking great.   

The seasonal aquatic fern, Salvinia (Salvinia molesta) quickly forms extensive floating mats on still waters and swamps, and can completely smother waterways and affect water quality.

In warm conditions, it can double in area within 2 weeks. It smothers or forces out native plants, can attract breeding mosquitoes, blocks dams and irrigation systems, removes oxygen from the water and creates a drowning risk for people and animals. And, it’s gotta go!

In early June 2018, Tauranga City Council, the Bay of Plenty Regional Council and Biosecurity New Zealand, began the first phase to contain and eradicate the infestation of this aggressive aquatic weed. It had spread over a 1 kilometre in the Wairakei Stream and threatened to spread further into other stream systems.

Local iwi, Ngā Pōtikī, were on site to help out during the week to monitor for eels during the removal operation and to ensure appropriate cultural processes were respected. The wider-iwi groups around Tauranga were also onsite to support Ngā Pōtikī and the eradication team at a karakia ceremony before the removal process began.


salvinia plants
The invasive Salvinia plant

The first stage of the removal process involved removal of the mass of salvinia by suction truck similar to that used for sewage spills.

“We’re very pleased with the process so far,” says John Sanson, Manager Recovery and Pest Management at MPI. “Virtually all the salvinia plants have been removed.”

As part of Tauranga City Council’s general weed management procedure they’ve sprayed herbicide on the banks to kill any remains of salvinia plants, deposited from recent flooding, and any other weeds on the banks and scrub near the stream. No spray has been used over the water.

Stage two is now underway, which involves regular and frequent checks to remove every last fragment of salvinia from the waterway and banks. These weekly checks will continue for several more months until no further plants are found.

“Following phase one, we’re only finding a few plants,” says John. “However, we must be sure to remove every remaining piece of salvinia because even very small fragments can survive and grow.”

The stream will be monitored over the next two to three years (stage three) to make sure all salvinia has been eradicated from the Wairakei Stream.

All going well, the team should be able to declare salvinia eradicated from the site around 2021/22.

Biosecurity New Zealand’s priority is to rid the country of every salvinia plant. If you have salvinia in a pond or aquarium on your property or know where it is growing, contact your local council or call Biosecurity New Zealand on 0800 80 99 66.

If you would like to know more about salvina, visit Biosecurity New Zealand.