Any road linking the Northern Distributor Road to the A47 west of Norwich would cause 'irreversible harm to the Wensum', it has been alleged.
Green Party councillors in Norwich have urged city council to shun proposals for the so-called western link of the road now known as the Broadland Northway.
The council's cabinet will this week decide on how to respond to the consultation into four separate options for the road, which will link the end of the NDR to the A47 west of the city.
And the council's Green group has urged them to reject all four possible routes across the Wensum Valley.
Group leader Denise Carlo said: 'The irreversible harm to the Wensum and Tud valleys, higher greenhouse gas emissions contributing to climate breakdown and extra new traffic are a high price for people and the environment to pay.'
It comes as another of the county's districts nailed its flag to the mast on the matter, with Broadland District Council giving its support to two of the proposed routes.
At a meeting of its cabinet, members voted to give equal support to routes C and D, the two routes closest to Norwich and both providing dual carriageways.
Ahead of discussing the response, the cabinet heard from Nick Adams, chairman of Ringland Parish Council on his concerns about the options.
The council's draft response, which was prepared by officers and based on views expressed by councillors in two other committees, identified route D as the preferred route.
He said: 'Ringland Parish Council respectfully asks that Broadland District Council to reconsider its choice of preferred route.
'Ringland Parish Council supports route C, despite the noise and pollution impact it will have on our village. We strongly believe the chosen route should be the one which delivers the best cost-benefit ratio for the whole of Norfolk, while having the least impact on the surrounding environment, ecology and residents.'
Meanwhile, Norwich City Council's cabinet will decide on its response Wednesday evening, with officers recommending they back any of the three dual carriageway options, but not support option A, a 7.2 mile single carriageway upgrade to the B1535 and A1067.
What are the options?
Option A: Single carriageway upgrade to A1067 to Lenwade and B1535 to A47 Wood Lane junction at Honingham, using existing bridge at Attlebridge. Cost: £60m.
Option B: New dual carriageway and A1067 upgrade. New route to east of Weston Longville linked to A47 at Wood Lane junction. Two alternatives to link to A1067. New junction at Attlebridge, using current bridge or viaduct over Wensum, joining A1067 east of Attlebridge. Cost: £155m.
Option C: New dual carriageway and A1067 upgrade. Link to A47 at Wood Lane. New junction to take route between Weston Longville and Ringland, crossing Wensum on 2,362ft long viaduct. Cost: £153m.
Option D: New dual carriageway and A1067 upgrade. New route west of Ringland, linked to A47 either at Taverham Road junction or closer to the current Easton roundabout junction, crossing Wensum on viaduct. Second viaduct over Tud. Cost: £161m.
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