Lake cleanup plan slammed as scam

A plan to use carp to get rid of exotic weeds from a polluted lake has been slammed by a freshwater scientist, who has described it as a ‘‘scam’’.

But the council worker behind the plan, who proposes getting the carp from his father’s business, says it is the cheapest option and would have long-term benefits.

Freshwater ecologist Dr Mike Joy said the carp would do nothing to fix the real problem at Dudding Lake in Rangitı¯kei – nutrient loss from farmland.

The lake is subject to a public health warning, with people advised not to swim there because of high levels of blue-green algae. The algae can produce toxins harmful to people and animals, causing rashes, nausea and numbness.

Dudding Lake is at risk of ‘‘flipping’’ – a scientific term to describe the transition of lakes from weed-dominated to algaedominated.

Discussions are set to take place between Horizons Regional and Rangitı¯kei District councils about what should be done to avoid the flip.

The district council has also applied to the Department of Conservation to release grass carp and silver carp into the lake, as well as the Taihape wastewater oxidation pond and Marton’s water reservoirs.

Joy said the weeds fed on the nutrients, and putting carp in would add another nutrient source.

‘‘All they’re going to do is eat the weed, s... out nutrients and then [weeds] are going to grow again. It’s not going to fix the problem, and potentially create more problems. It’s just wasting ratepayer money on a stupid scam.’’

Ka¯ kahi, or freshwater mussels, probably lived in the area, but the species was threatened and in decline because waterways were being polluted, he said. They did filter water, but the amount needed to do the job at Dudding Lake would be massive, he said.

The consent application names the district council’s strategy and community planning manager Blair Jamieson as the contact person for the application.

Jamieson used to work for New Zealand Waterways Restoration, a company that breeds and releases carp and that was founded and is majority-owned by his father, Gray Jamieson.

The consent application identifies New Zealand Waterways Restoration as the source of the carp.

In an interview, Blair Jamieson made multiple references to his history in the industry, and directed Stuff to New Zealand Waterways Restoration’s website to learn more about the carp.

The carp plan would be a good one for Dudding Lake, he said.

The base is dominated by non-native weeds that grow high and take over from native ones.

They also choke out ka¯ kahi.

Blair Jamieson said the carp, which do not breed in New Zealand waters, would act as a kind of lawnmower, eating the weeds and creating space for native weed species and ka¯ kahi to flourish.

Using alum to reduce the algae, or killing off the weeds with chemicals, created other problems, while carp would cost less and could be captured live once they had served their purpose, he said.

‘‘The carp is a temporary issue.’’