Boaties warned to wash boats

New Zealand boaties are being warned to carefully wash down their boats before taking them into new lakes or rivers in the Bay of Plenty.

With the trout-fishing season starting on October 1, Environment Bay of Plenty wants to remind boat users of the “absolute importance” of checking boats, trailers and even anchor chains for exotic aquatic weeds and pest fish.

Environment Bay of Plenty pest animal coordinator David Moore says the efforts of diligent boaties have so far kept Rotorua’s lakes free of the environmentally harmful pest koi carp. But it was all too easy for eggs or small fish to hide in strands of lake weed.

Lake Taupo and lakes in the Waikato host koi carp and “we don’t want them here”, he says. “It is critical that everyone continues to check for the pest fish. We can’t afford to get complacent.”

Koi carp were probably brought to New Zealand with stocks of goldfish. Wild stock is thought to have escaped from ponds. Koi carp degrade water quality and are a serious threat to native freshwater marine life. They grub for food from the bottom sediments of lakes and ponds, uprooting plants and stirring up the water, which reduces water quality.

You can be fined up to $5000 for possessing or rearing them.

Environment Bay of Plenty is also concerned at the ease with which aquatic weeds can be transferred from one lake to another. Some Rotorua lakes are free of the more invasive exotic submerged macrophytes, or oxygen weeds, says pest plant coordinator John Mather. 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 one boat to bring it in.”

Mr Mather asks boaties to inspect boats, trailers, jet units and anchor chains before taking their boats into a new water-body. “Some of the lakes now host tall underwater forests of exotic weeds, which have taken over from the native plant life. We don’t want these weeds to spread even further – and boaties have a part of play in that.”

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