Water net

Forest and Bird, Volume 22, Issue 2, 1 May 1991, Page 4

Water net

Basil Graeme

| N 1986 WATER NET, (Hydrodictyon reticulation), was first found in Tauranga by Ministry of Agriculture and Fisheries officials, who believe that it was accidentally imported with plants or fish by an aquarium trade importer. At that stage it was well established in ponds, aquariums and in the entire stream of the catchment where it was discovered. From there it has now spread to the Rotorua lakes, Taupo, and even the Maketu Estuary. It is predicted to spread into the Waikato River and be a major weed within the next two years. Water net's algal filaments form a green mesh like a sausage-shaped hairnet, up to 20 cm long. It was first recorded in Chinese writing as a pest of rice paddy fields, over a thousand years ago. This summer, water net has grown prolif-

icly in the shallow water of Lake Rotorua, its slimy strands spoiling the pleasure of bathers, anglers and boaties. When it grows densely, small fish can become entrapped and die. Water net has an incredible capacity to multiply vegetatively from every cell. It grows prodigiously over the warm summer months, and remains in significant quantities during winter. This pest seems set to invade lakes and dams throughout New Zealand. There is no known method of control. The algal invasion highlights the ease with which pests can enter New Zealand, and reinforces Forest and Bird’s opinion that much tougher import controls are needed. gy