Progress on weaving solution

First uwhi trial at midway point of pest and weed control project.

Three images, including a group of people stand before a green tarpaulin beside a lake; a close up of uwhi; and Lake Rotoiti with uwhi in the foreground.
Uwhi laid out before being taken out by boat and laid on the lakebed by divers. Photo: William Anaruexpand/collapse

Our January blog included a story about uwhi being trialled to combat exotic pest weed in our lakes. The project is a collaboration between Toitū Te Whenua Land Information and Te Arawa Lakes Trust. Weavers’ group, Te Roopu Raranga ki Rotorua was contracted to design and weave the uwhi. The group applied historical mātauranga together with their collective skills and extensive experience to produce different versions of uwhi for consideration. Eventually three designs were chosen for use in the trials.

In a project led by Te Arawa Lakes Trust, one each of the three selected uwhi designs, and one hessian mat, were laid in three lakes – Rotoiti and Tarawera late last year, and in Rotomā in Feb 2022. The main advantage of using natural fibrous plants like harakeke (flax) or hessian, is that it is biodegradable, and will break down in the lake without the need for removal.

Uwhi are designed to prevent photosynthesis in aquatic pest weeds, in a similar way to weed matting that you might have in your garden. Te Arawa Lakes biosecurity manager, William Anaru, explains that “the matting laid on the lakebed will block out the sunlight and suppress pest weed growth, allowing buried native weed seedlings to grow and recolonise.”

Uwhi are designed to prevent photosynthesis in aquatic pest weeds.

Aquatic plants are important to the health of our lakes and waterways by improving water quality and providing habitat for wildlife. Unfortunately, it has been observed that the larger non-native aquatic plants smother the smaller natives. As they spread, they form a dense weed wall which prevents native species like koura (freshwater crayfish, Paranephrops planifrons) from accessing the shallow waters where they gather to feed.

The team are about halfway through the 12-month monitoring phase of the uwhi project. Two of the four designs are holding together well, one design is not doing as well. The least stable of the four are the hessian mats which are already breaking down.

- Niki Partsch