An infestation of the aquatic pest plant hornwort has been found in Rotoruaâ s Lake Okareka.
The invasive weed, which has not been seen in Lake Okareka before, was found by the skipper of the Duck tourist vehicle last month.
It's one of the most invasive aquatic weeds because it isn't limited by water depth.
The Bay of Plenty Regional Council says it can spread easily and rapidly displaces native vegetation in both shallow and deep water.
NIWA scientists are helping to work out how best to manage the problem.