Lake Wainamu restoration efforts show positive results

A seven year effort by Auckland Council to rid Lake Wainamu of exotic fish and plants has resulted in ecological and recreational benefits for the environment.

Located near Te Henga (Bethells Beach), picturesque Lake Wainamu is a popular spot for families and recreational users. Also known for its extensive sand dunes, the lake is one of 11 high conservation value lakes in the Auckland region.

Exotic fish, egeria (oxygen weed) and hornwort had overrun the lake so council’s biosecurity and freshwater science teams implemented pest management programmes to restore the lake’s ecosystem and allow native aquatic vegetation and fish to re-establish.

“An exotic fish removal programme was introduced in 2004 and twice a year for the first three years of the programme, gill nets were set around the lake over a one-week period,” says Auckland Council freshwater scientist Graham Surrey.

“The nets, which are now set annually, are cleared by volunteers from Auckland Council and over the last seven years more than 15,000 exotic fish have been removed.”

To complement the fish removal programme, a weed eradication programme was introduced in 2009 to address problems with egeria and hornwort choking the lake.

“We investigated the use of aquatic herbicides and mechanical removal methods to eliminate the weeds but introducing grass carp was more cost effective and environmentally sustainable,” says Mr Surrey.

“Grass carp have been widely used for weed control in New Zealand but are unable to breed in the wild. Their introduction into the lake has been so successful that the egeria weed has been almost entirely eradicated and we are now seeing the first signs that native freshwater plants are beginning to re-establish.

“Hopefully we will soon be in a position to remove the grass carp and have native aquatic plants flourish once more within the lake,” says Mr Surrey.

Parks and Heritage Forum chair Sandra Coney says the pest removal programme’s success reflects on everyone who contributed over the last seven years.

“The preservation of our natural lakes has huge ecological and recreational benefits and it’s important that we all play our part to keep them safe and clean for future generations.

“While fishing is not permitted at Lake Wainamu, it’s important to clean any boats or other recreational equipment before and after use as this type of weed is easily spread.”

Editors Note:

July is New Zealand Biosecurity Month. Auckland Council’s biosecurity team work on a range of initiatives to protect our natural environment and primary production, including controlling possums, feral goats, pigs and deer, pest plants and kauri dieback disease.