MAF Biosecurity New Zealand lifts restrictions on Centennial Park Lake

24 February 2009

MAF Biosecurity New Zealand (MAFBNZ) has lifted the Restricted Place notice placed on Centennial Park Lake, Timaru after the latest survey revealed no visible signs of the highly invasive freshwater weed hornwort (Ceratophyllum demersum).

The Restricted Place notice closed the lake and the north branch of the Otipua Stream to all use (including paddling, fishing, kayaking and swimming) in February 2006 after hornwort was discovered there. Closing the lake enabled MAFBNZ to carry out carry out control work and minimise the risk of the weed spreading to other waterways.

"Meticulous searching by divers from the National Institute of Water and Atmospheric Research in November found no sign of hornwort in the lake or in the outlet stream. Only elodea and curled pondweed were noted. This means the lake can return to normal use by members of the public," said MAFBNZ Senior Adviser, Pest Management, Victoria Lamb.

"We are very pleased with the outcome of the hornwort control work in Centennial Lake, as it significantly reduces the risk of hornwort being spread to other South Island water-bodies.

Hornwort is currently widely established in the North Island. It has only been found at two sites in the South Island - near Motueka and in Centennial Park Lake, Timaru.

Ms Lamb said another survey of both the lake and the outlet stream is planned for late summer 2009. Annual surveys of the lake and stream will continue for five years to 2014, and if no hornwort is found it will be declared eradicated from the site.

Hornwort is a free floating plant with no roots. It has long, dark green stems with forked leaves arranged in whorls of 7-12. Its stems are easily broken and can contaminate boats, fishing and recreational equipment, and can survive for several months in wet spots such as under the floor or in the anchor well of boats. It can also be spread through the release of aquarium or pond contents into waterways.

Ms Lamb said good hygiene practices can help slow the spread of hornwort and other freshwater pests such as didymo.

"Before leaving any waterway people should check all equipment they have used in the water, remove any visible fragments of weed, clean if necessary, and leave to dry. 

"They can also help by not empting fish tanks into or near a waterway and not draining any ponds into waterways," said Ms Lamb.

All sightings in the South Island should be reported to MAF Biosecurity New Zealand on 0800 80 99 66. In the North Island contact the relevant regional council to determine the status of the species and responsibility for control and/or advice on control.

For more information contact:
Judith Hamblyn, Senior Communications Adviser, MAF Biosecurity New Zealand, Ph 04 8940687 or 029 894 0687