Weed-spraying on Lake Benmore's Ahuriri arm, delayed because of unsuitable weather conditions in January, will take place after the Easter holiday in April.
A helicopter would be used to spray the herbicide diquat in a gel form, with a tracer dye to judge its dilution and dispersion.
Land Information New Zealand (Linz) manager of Crown property Bill Naik said the timing of the spraying was later than usual because weather and water conditions could significantly affect its success in lakes.
This year, floods in the Ahuriri River during January and high winds meant it was unsuitable to carry out the operation.
Radio announcements will advise lake users when the spraying is due to take place.
Public notices will also be put in newspapers, on the Linz website and warning signs put up at public boat ramps during treatment.
The annual programme to kill lagarosiphon weed is a joint project between Linz and Meridian Energy Ltd.