A trial by Waikato Regional Council to trap koi carp and recycle the pest into potting mix, is about to begin at Lake Waikare.

The lake is one of the major breeding sites for carp with large numbers of the fish entering the lake through one particular fish pass.

The council is putting a special fish trap and digester in and beside the fish pass to catch and kill the fish and mulch them into a nutrient-rich potting mix.

Koi carp compete with native species for food and stir up sediment which causes the growth of toxic algae.

A freshwater scientist Bruno David hopes the system will be almost fully functioning by the end of November.