"In a fortnight, we will have to turn off all irrigation," he said. "It really is an extreme climate event that we have not seen since the dam was built."
The dam serves its 250 farmer shareholders, who have 16,000ha under irrigation.
For drought, or "adverse event" declarations, the Government classifies how serious the problem is and how localised it is.
If the Government declares a medium-scale adverse event, much of the support made available to affected farmers will be similar to the support made to any business or family in adversity.
Under certain circumstances, drought-affected farmers can defer tax payments and assistance is available through the Rural Support Trust.
Last month, Westpac said dry weather throughout much of New Zealand was likely to take a "significant chunk" out of GDP growth over the first and second quarters.
Federated Farmers said conditions were getting drier in Marlborough and nine of the province's 16 consent areas have had their right to irrigate suspended.
Blenheim has had its lowest rainfall in 85 years over the July 2014- January 2015 period, receiving just 35 per cent of the long-term average rainfall of 381mm.
Other areas of Marlborough are also suffering significantly lower rainfall, including Avon Valley, which has received only 245mm of rainfall - 53 per cent of the long-term average.
The Marlborough branch of Federated Farmers has established a local drought committee to keep water users up to date.
