A unique weed harvesting machine, described by its skipper as something out of Waterworld, is helping restore Lake Horowhenua (Punahau). The contraption, part boat and part tractor, moves slowly across the lake, using paddle steamer-like wheels and sharp teeth to cut and collect up to ten tonnes of aquatic weeds daily. Built in the U.S. by Aquarius Systems and one of only two in New Zealand, the harvester trims weeds just above the lake bed. This ongoing project, a collaboration between Horizons Regional Council and the lake’s owners, Muaūpoko, aims to manage the excessive weed growth, which alters the water’s pH and contributes to pollution. Despite four years of mowing, the weed volume remains high, but overall water quality is gradually improving.
Punahau has long suffered from pollution due to farming runoff and historical sewage discharge, earning it a reputation as one of New Zealand’s most contaminated lakes. However, efforts to restore its health are showing progress, with the return of native plants and fish like grey mullets. Muaūpoko leaders emphasize the lake’s spiritual and cultural significance, calling its restoration a step toward healing both the water and their people. Last year, over 400 tonnes of weeds were removed, a record likely to be surpassed this summer. The harvested weeds are repurposed as compost, ensuring the cleanup efforts also support sustainability.