Opponents to the WCO, including horticulturists and growers, have said it could result in job losses, but Dr Joy said it was a matter of weighing up whether they wanted to have employment now at the expense of having no rivers in the future.
"Jobs in these industries are not that great anyway - they are not appealing and usually not very well paid.
"If these industries can't work within the limits they need to do something about it and not destroy the environment."
One plank in the argument against the WCO was that the Hawke's Bay Regional Council-led TANK process was set to achieve the protections sought in the WCO but Dr Joy rejected the effectiveness of such processes.
"Projects like TANK are a generally a failure everywhere.
"The idea is great, that the community makes the decisions, but the reality is they are dominated by industry which has all the science, power and resources.
"Who is protecting the river on behalf of Joe Bloggs? No one except some pushed to the limit iwi or NGO."
In Hawke's Bay, like in Canterbury, Dr Joy said the impact of commercial activities on the rivers had gone too far, and it was time to pull those activities back.