Lawyers are being brought in after councils across Norfolk were told they would have to halt decisions over hundreds of homes in the county - amid pollution concerns.
Government advisor Natural England informed Norfolk councils they must not grant planning permission for any schemes involving 'overnight accommodation', until it can prove developments would not lead to more nutrients flowing into waterways.
That is because of concerns over phosphates and nutrients flowing into the Broads and River Wensum.
Natural England and DEFRA say councils need to make assessments against which developers can prove their schemes are nutrient neutral - by providing mitigation if necessary.
Councils says they do not currently have the expertise to make such assessments and to decide what mitigation would be needed.
While they work out what to do, they have suspended granting of permission for homes, student housing, care homes and campsites within the catchment areas of those waterways.
And councils are to meet next week to discuss what their next move is, with the help of lawyers.
John Fuller, leader of South Norfolk Council, said: "The whole country is grappling with how to reduce effluence going into our rivers and it's likely to be a 30 year intensive campaign involving many millions of pounds to achieve that.
"It is wholly unrealistic for Natural England and DEFRA to put in regulations, which might be appropriate in 30 years, today."
He said their methodology was "leaky" and transitionary arrangements should have been brought in, rather than suddenly leaving councils scrambling to establish what needs to be done.
He said: "I am convening a meeting of all our local councils in Norfolk where they will consider legal opinion of counsel as to what the appropriate next steps will take."
The pollution which Natural England is concerned about is generally from sewage treatment, septic tanks, farming and industry.
It reduces the oxygen in the water and makes it harder for aquatic species to survive.
Wastewater from new developments can exacerbate the issue.
Mitigation measures could include creating new wetlands, woodland or grasslands, or building environmentally-friendly drainage systems.
What does Anglian Water say?
Water company Anglian Water says it would be able to expand or improve treatment processes in Norfolk to cope with increased nutrients in wastewater.
The company says it will be down to Natural England and local councils to determine what nutrient neutrality is, how it will be calculated and any increase in nutrients mitigated for.
The company says it will accept flows from new developments once that process is satisfactorily completed.
A spokesperson said: "The nutrient reduction targets that impact on the capacity of water recycling centres are set by Natural England and the Environment Agency and inform our Asset Management Plan, currently running from 2020-2025.
“We fully support sustainable development in our region, and where population and economic growth has the potential to cause higher levels of nutrients in wastewater, we expand or optimise our treatment processes to cope with this.
"Our processes have additional headroom in their capacity to allow for this.
"This is why, for the Broads in particular, we know that our treatment works are not contributing to nutrients above permissible levels as set out in our permits."
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