Two aquatic weeds, hornwort and egeria densa, have been found for the first time in Rotorua's Lake Rotomā - inside Bay of Plenty Regional Council's weed cordon.
The two weeds were found by summer students who were working for the Regional Council at Lake Rotomā advising boaties about checking and cleaning boats of any weed fragments before they enter the water.
Regional Council General Manager of Natural Resource Operations, Warwick Murray, said he was disappointed the weeds had turned up in the lake but pleased that the weed cordon was working to keeping aquatic weeds out of the lake.
Weed cordons that trap weed fragments have been installed on four lakes. Rotomā and Ōkataina have two each, and Ōkāreka and Rotoehu each have one cordon. They are a first in the world, and are successfully preventing weeds spreading into lakes from boats and equipment.
"It's a timely reminder of how important it is to clean, check and dry boats, trailers and anchor wells before you leave a lake to make sure you don't carry unwanted hitchhikers into another lake. There are signs up at all Rotomā boat ramps reminding boaties to check, clean and dry their equipment, not just let the weed cordon do the job for them," Mr Murray said.
"Rotomā is a very beautiful lake, and has been free of these weeds that are already in nearby lakes. Lake Rotoehu has hornwort in abundance. The weed cordons are a stopgap against laziness, ignorance and oversight, but it is the responsibility of all boat owners and users to ensure these lakes remain weed-free."
He said the Regional Council had done extensive checks and had not found any sign of the two weeds in the rest of the lake so he was hopeful the cordon had done its job. The lake would be monitored for the next five weeks to ensure the weed had not established elsewhere.
Hornwort and egeria densa are 'containment pests' - weeds which cannot be eradicated from the region but need to be contained to limit their impact on other lakes. They are banned from sale, propagation and distribution throughout New Zealand. The two plants are very distinctive and different from the native species lagarosiphon major, which is already in Lake Rotomā.
In March 2010 hornwort was found in Lake Ōkataina, and was suspected to be in Lake Ōkāreka last summer, but due to an infestation of egeria densa, the extent of the spread could not be measured.
Mr Murray said 85 percent of people interviewed last summer around the Rotorua lakes had a high level of interest in aquatic pest issues, and 45 percent checked and cleaned their boats before moving to another lake.
At Lake Rotomā this summer, 51 percent of people interviewed were unaware or had a low awareness of aquatic weed issues, but 49 percent said they had a moderate or high awareness.