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More risk of aquatic weeds in lakes

More risk of aquatic weeds in lakes

For immediate release: Tuesday 16 December 2003 Some of Rotorua’s more pristine lakes are in danger of having their ecological balance upset by aquatic weeds if boaties who usually go to Lake Rotoiti decide to try out other lakes this summer.

The aquatic weed Lagarosiphon is widespread throughout the Bay of Plenty but – so far - does not grow in Lake Rotomahana. Its stems grow up to five metres long.

Recreational boaties may be put off using Lake Rotoiti if the lake suffers from widespread algal blooms again this summer, says Environment Bay of Plenty pest plant coordinator John Mather. He is concerned the shift will increase the chance of boats bringing new and potentially harmful weeds into lakes that do not already have them.

Lake Rotoiti already hosts “pretty much the full range” of aquatic weeds in the region, he explains, so its popularity doesn’t put it at any greater risk. But other lakes are free of the more invasive exotic macrophytes, or oxygen weeds. Lake Rotomahana, for example, does not have any weeds of this type. Lake Rotoma has one species but not the whole range.

“Yet that can change very quickly,” he says. “All it takes is for one boat to bring a new weed in. Some of the lakes already host tall underwater forests of exotic weeds, which have taken over from the native plant life. We don’t want that to keep on happening.”

Environment Bay of Plenty and the Department of Conservation will work together over summer to promote the issue to boat users. They will give away key rings and bumper stickers printed with a message urging skippers to carefully clean their boats after use.

Mr Mather says it is important to carefully inspect boats, including propellers and anchor chains, as well as trailers, before taking them into a new water-body. “People need to pick off any weeds and if necessary wash down their boats. We don’t want these weeds to spread even further – and boaties have a large part of play in that.”

The eggs of pest fish like koi carp and catfish also hide in strands of weed. While Lake Taupo and lakes in the Waikato region have koi carp, Rotorua’s lakes are still free of them.

Koi carp grub for food from the bottom sediments of lakes and ponds, uprooting plants and stirring up the water, reducing water quality. Environment Bay of Plenty works in partnership with the Department of Conservation to keep the region both koi carp and catfish free. Between December and February, they jointly monitor the Rotorua lakes for the pest fish.

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