Aquatic pest found in Lake Okareka

An infestation of the aquatic pest plant hornwort has been found in Rotorua's Lake Ōkāreka.

The invasive weed, which has not been seen in Lake Ōkāreka before, was found by the skipper of the Duck tourist vehicle last month.

Bay of Plenty Regional Council Land Resources Manager Greg Corbett said hornwort (Ceratophyllum demersum) was one of the most invasive aquatic weeds, as it was not limited by water depth as other invasive species were. It could spread easily and rapidly displaced native vegetation in both shallow and deep water.

"Regional Council staff, assisted by NIWA scientists, have been investigating to assess the full extent of the incursion and how to manage it," he said.

"Fragments have been found in several places around the lake, including some within the lake's weed cordon in the emergent raupo, one in front of the Steep Street reserve and many small plants and fragments in a north-western bay between Boyes beach and the Department of Conservation camp."

He said no fragments had washed up on any beaches so far, indicating that the main infestation was likely to be within the north-western bay where most fragments were found.

Once the full extent of the incursion was known, a response plan would be developed, Mr Corbett said.

"It is likely that hornwort may have been present in the lake for five to seven years, so it was not stopped by the weed cordon at Acacia Bay which was established more recently."

Boaties should always inspect trailers, engine wells, anchors, propellers, fishing gear and other wet equipment such as waders to ensure they are not carrying either weed fragments or pest fish species before they leave lakes or other waterways. All equipment should be thoroughly cleaned before it is used again, Mr Corbett said.