Maintaining Weed Free Irrigation & Farm Dams


with Irrigation Lakes & Farm Dams


Due to our economic focus on primary industries New Zealand has become dotted with storage reservoirs (artificial lakes, or modified-natural lakes with raised water-levels), ranging in size from small farm dams, through to the 7,500-hectare lakes. These storage lakes and farm dams are used for irrigation, as they allow water to be harvested during times of plenty and released at times most beneficial to farmers. NZ Waterways regularly visits these storage sites; seeing first hand the damage caused by pest weeds (notably interfering with pumping functions and collapsing waterways). Grass carp should be the preferred option, and are generally contained by way of outlet screens. Other aquatic weed control methods such as the use of herbicides and mechanical removal of nuisance weeds result in considerable loss of aquatic life and result in degradation of the habitat through rotting vegetation and sediments – not to mention herbicide not complimenting grass growth.

NZ Waterways has supplied Grass Carp to Irrigation Dams in the Hawkes Bay’s, namely Te Tua and Washpool Station. Similarly to the national experience, we are seeing aquatic weeds being able to decrease water storage capacity by 20%. We are also presently working with a Canterbury company with a view to set up the farming of Grass Carp in their irrigation Dams.



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