Regional council checking garden ponds for harmful invaders

Bay of Plenty Regional Council is taking a closer look at what’s in backyard ornamental ponds in the Rotorua area to protect lakes from potentially harmful invaders.

Aquatic pest plants and fish can make their way from garden ponds into the lakes from flooding, or even from owners moving the contents of their pools into lakes and rivers.

Pest Plant Officer Richard Mallinson said ornamental ponds posed a high risk for incursions of pests, and some people did not think about the risks when they dumped pond contents into streams or lakes.

Lake Ōkāreka was chosen as an initial survey point because it was currently free of hornwort, a prolific weed found in Lakes Rotorua, Rotoehu, Tarawera and Rotoiti, and had no confirmed infestations of pest fish such as koi carp, catfish, rudd and tench. A 1980s infestation of Marshwort that originated from a nearby pond had been eradicated.

“New exotic species that are introduced into the lake would compete with native species and alter the entire fragile lake ecosystem,” Mr Mallinson said.

Residents in the Ōkāreka area were sent a letter and leaflets about the survey and a contractor visited all the properties to discuss the ponds and their contents.

“Lake Ōkāreka residents were very interested and positive during the audit and were keen to ask questions and be involved in what this audit was trying to achieve.”

Of the 30 ponds found, 13 contained goldfish which are currently also found in Lake Ōkāreka. He said the Bay of Plenty was lucky not to have destructive koi carp, which were found in large numbers in the Waikato. Koi can spread as eggs attached to weed.

The programme has been designed to pre-empt any possible infestations of pest weed or fish so they can be dealt with before they become an issue in the lakes.

[For more information contact Bay of Plenty Regional Council]