"The river supports an agricultural landscape which people know and love as iconically Hawke's Bay, with river water being used by local orchards, vineyards and cropping farmers for over 150 years," Mr Curtis said.
"This landscape and the jobs it creates is now under threat from the water conservation order."
Water take from the Ngaruroro River would be reduced from around 6300 l/s (6.3 cumecs) to just under 1600 l/s (1.6 cumecs) when the river flow is less than 70 cumecs - as it had been during the "critical time for crops" between October 2016 and April 2017.
This equated to the 7300 ha currently irrigated by water from the Ngaruroro River, being halved.
By these numbers, Mr Curtis said the 1800 jobs lost would be around half of the estimated 3650 jobs currently supported by irrigated land from the two rivers on the Heretaunga Plains, and would include vineyard and orchard workers, staff working in packhouses, and vegetable processors.
His fears were echoed by Hawke's Bay fruitgrowers president Lesley Wilson, who said their association would be opposing the order.
"We need to look through the details but it appears that the allocation numbers [of water] are well below what is currently being taken and that will of course have an impact on fruit production, and therefore jobs in Hawke's Bay," she said.
"We are considering not objecting to a WCO from Whanawhana up but more research needs to be done before we decide on that."
The WCO was a "blunt tool", she said, compared to the TANK method which was a "far more community focused process and will have an outcome that benefits everybody".
However those supporting the application have disputed these concerns, labelling them as "cynical scaremongering".
The water conservation order was jointly lodged by the NZ Fish and Game Council, Hawke's Bay Fish and Game Council, Ngāti Hori ki Kohupatiki, Whitewater NZ, Jet Boating NZ and the Royal Forest and Bird Protection Society of NZ.
Application project manager and director of the Catalyst Group Greg Carlyon said the application was clear that water storage for irrigators could be provided.
"The application has been very specific in confirming the rights and interests of irrigators and water users and is clear that current rights will not be unwound as a consequence of the Order. Only the [Hawke's Bay Regional Council] can do this, and we are not aware that this is their intention."
Forest and Bird freshwater conservation advocate Annabeth Cohen said the Ngaruroro River was a special freshwater habitat, which they were taking the opportunity to protect.
She said the lower reaches of the Ngaruroro was most at risk of losing its outstanding significant values - Irrigation NZ agreed the WCO should apply to the rivers upper reaches, but maybe not its lower as these parts had been "highly modified".
Fish and Game communications manager Don Rood said they did not believe the projected number of job losses was accurate, and that it appeared the group was putting the economy ahead of the environment.
Waterways needed to be better protected, "they're not there just to be taken and exploited and sprayed over some dry paddock when someone feels like it".
Whitewater New Zealand president Nigel Parry said as "pressure on our rivers continues to grow, it is sensible to manage to practical environmental limits and maintain the health of the river for future generations".
A special tribunal has been appointed to consider the application, and will hold a hearing on it later this year.
¦Submissions on the application close on Friday, August 24. They can be made at
epa.govt.nz/Pages/default.aspx.
