In May 2009, grass carp were released into Lake Roto-otuauru (Swan) on the Poutō peninsula to control the very invasive aquatic plants hornwort and egeria (oxygen weed). Lake Swan is the only lake on the Poutō peninsula to have hornwort so it is vital to control it before it spreads to other neighbouring, high value lakes.
Monitoring carried out in March 2010 showed that most of the egeria and approximately 50% of the hornwort have already been removed by the grass carp.
In June 2010, grass carp were released into Lake Heather, north of Kaitāia. This high value dune lake is also infested with hornwort and egeria and grass carp are expected to have an impact on these weeds over the coming summer months. Fish will be removed from the lakes once the pest plants have been eradicated, which is predicted to take up to five years.
Photo: Lake Ngatu fish survey