Concerns are mounting that the Long Stratton bypass could be hampered by the limbo over granting planning applications for homes in Norfolk.
Council leaders fear the planning application for the road, which is linked to construction of 1,800 new homes in the area, could be held up due to the issue around nutrient neutrality.
The Department for Transport last year pledged £26.2m towards the £37.4m cost of the two-and-a-half mile A140 bypass.
A wedge of funding for the road is due to come from local developer contributions and Community Infrastructure Levy cash - money which hinges on homes being built.
But plans for the road, along with an associated 1,875 homes, a primary school and 30 acres of employment land have yet to be approved.
And council leaders are worried they will be caught up in delays triggered by Natural England's directive to all Norfolk councils.
The councils have been told they must not grant planning permission for schemes involving 'overnight accommodation' within catchment areas of the Broads and River Wensum, until they can prove they would not cause more nutrients to flow into waterways.
That is because excessive nutrients trigger algal blooms, which can harm aquatic species.
Council leaders from Norwich, Broadland and South Norfolk have written to cabinet ministers Michael Gove and George Eustice, urging them to intervene on the issue.
They want them to order Natural England to withdraw the letter and give councils a year to get necessary procedures, including mitigation measures, in place.
That letter, signed by South Norfolk Council leader John Fuller, Norwich City Council leader Alan Waters and Broadland District Council leader Shaun Vincent, states that there are "particular concerns" about the impact of delay on the delivery of the bypass.
It says: "The scheme aims to alleviate a main bottleneck on the A140, linking the regional centres of Norwich and Ipswich, whilst removing significant volumes of traffic from Long Stratton, with consequent environmental benefits.
"The bypass supports, but is also reliant on funding from, delivery of 1,800 plus homes plus new employment opportunities.
"Consequently, the yet to be determined planning application for the bypass is part of the overall application for the growth package."
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