Killing koi could be the key to saving the lakes

Native fish and plants are in decline in most New Zealand lakes and waterways. Pest fish and invasive weeds out-compete native species, and they also alter the environment to cause proliferation of harmful algal blooms.

Nutrient run-off from farms has created an ideal habitat for pest fish, such as koi carp, to thrive, but University of Waikato researchers are hopeful removing pest fish can help restore some lakes without forcing farmers to drastically reduce their fertiliser use.

To tackle the problem, Dr Adam Daniel has researched koi carp movements, and designed and installed a barrier on an outlet stream coming from Lake Ohinewai – near Huntly.

 The one-way barrier placed at an outlet stream allows koi carp to move out of the lake but not return. Removing the remaining koi carp population and measuring the resulting water quality may help provide a template for lake and waterway restoration.

The project is part of LERNZ Lake Ecosystem Restoration New Zealand, based at the University of Waikato, which has $10 million over 10 years to research the threats posed by algal blooms, pest fish and other invasive species – and how to address those threats.

Funded by the Ministry of Science and Innovation, the programme focuses on the Rotorua Lakes but will have nationwide and international application.

Professor David Hamilton, Dr Deniz Özkundakci and Dr Daniel are running the programme, which has input from regional councils, community groups, the water industry and other organisations, as it is those groups that will ultimately benefit from the research work.

The researchers have also developed monitoring tools to detect and understand more about algal blooms, which have in some cases resulted in water supply closure, cattle deaths and closures of lakes for recreational activities.

That work is also providing benefits in China, where monitors have been installed in Taihu Lake to provide information about blooms of blue-green algae which affect drinking water supplies for more than five million people.