Rosie Bay re-opened to the public
Date: 19 March 2008
Easter visitors to Lake Waikaremoana will be able to access Rosie Bay on the eastern side of the lake, eight years after the inlet was closed to the public due to a water weed infestation.
Lagarosiphon weeding at Rosie Bay
Department of Conservation (DOC) Aniwaniwa Area Manager, Glenn Mitchell said today that being able to declare the bay free of Lagarosiphon major was a tribute to the persistence of DOC and Conservation Corps workers, and a warning of how easy it is for unwanted organisms to be spread to remote areas.
"We discovered lagarosiphon in Rosie Bay during weed monitoring in March 1999. As other areas with infestations of this weed can testify, it is a plant that can spread very quickly, clogging up waterways, disrupting boating, swimming and fishing. There was also concern at the potential for a heavy infestation to affect the Waikaremoana Power Scheme. From an ecological perspective, lagarosiphon displaces native plants and reduces oxygen through the effect of rotting dead plants," Mr Mitchell said.
Lagarosiphon weeding at Rosie Bay
Due to their remote locations, Lakes Waikaremoana and nearby Waikareiti are relatively free of exotic water weeds, and in that respect, are something of a rarity in the North Island. As surveys showed that the weed had not spread beyond Rosie Bay, DOC staff attempted a task that had never been successfully achieved before in New Zealand - eradication of lagarosiphon from a substantial water way.
The bay was closed to the public and the weeding began. Lagarosiphon does not set seed in New Zealand, but can spread from small stems. A team of DOC divers working with Aniwaniwa staff and the local Ministry of Youth Affairs Conservation Corps, started a regular programme of weeding Rosie Bay. Early efforts resulted in tonnes of material being removed. The heaviest infestations in shallow water were covered with matting to exclude light.
In 2003 when matting was lifted, the lake bottom was clear of vegetation and in following weeks, was quickly colonised by native aquatic plants. In regular surveys, divers checking areas not covered by the mats found steadily decreasing plant numbers. January 2006 was the last time a lagarosiphon plant was found in Rosie Bay, and subsequent surveys have all had a nil result.
"We are confident that lagarosiphon has been eradicated from Lake Waikaremoana and all barriers to Rosie will be removed before Easter. Our major concern is that re-infestation could occur at any time unless people take care to ensure vehicles, boats and equipment are completely weed-free before they are taken into the lake," Mr Mitchell said.
"We were lucky that the geography of Rosie Bay allowed us to deal with the weed in a confined area of the lake. Only one plant has been found elsewhere in the lake during our regular weed monitoring. Yearly surveillance of all high risk sites for aquatic weeds around Waikaremoana will continue to be undertaken.
"Eradicating lagarosiphon from Waikaremoana has required patience, persistence and work in snow, rain, wind and occasional sunshine. After eight years of painstaking weeding and monitoring, staff are in no hurry to repeat the experience, particularly as it has taken them away from other conservation work. We strongly urge people visiting Lake Waikaremoana to take particular care to ensure that no further weeds are introduced to one of the few, relatively pristine large waterways left in the North Island," Mr Mitchell said.
ENDS