Weed invasion

A highly invasive aquatic weed found in a man-made Taranaki lake could threaten other lakes if allowed to spread. An annual survey monitoring of Lake Rotorangi’s water quality has found hornwort in the lake, the Taranaki Regional Council’s policy and planning meeting was told. Hornwort is considered by the National Institute of Water and Atmospheric Research as the country’s worst submerged weed. It can grow underwater as high as a three storey building and has been found up to 10 metres tall. Broken off fragments of the weed can be easily transported by boat trailers, fishing gear, float planes and weed harvesters to nearby lakes, scientists say. The plant was reported growing in Lake Rotorangi, a hydro lake near Patea, in 2012 and also 2015. It is not considered a threat to hydro electric generation on the lake but could pose a greater risk if it established in other Taranaki lakes, the meeting was told. It was first reported growing in Hawke’s Bay and is now established in 30 North Island lakes. In 2002 it was detected in the South Island.