Campaigners are hoping to lodge an appeal against the by-pass decision.
David Gate, of campaign group Transport Solutions for Lancaster and Morecambe, said: “We shall look at the decision and take legal advice. Were all the issues considered properly?
“For example, otters are protected under European law.
“The council denied they are there, but there is proof that they are.
“How can the council protect them if they don’t know where they are?”
Green Party member, Prof John Whitelegg, said: “Discussion has been going on for some time about what would happen if the road went ahead.
“It is likely that there are grounds for a legal challenge.
“The decision is faulty as far as I am concerned.”
Prof Whitelegg said the city council, in its only ever debate of the bypass in 2007, voted not to support the scheme.
This was being “conveniently forgotten”, Prof Whitelegg said, and could be grounds for a legal fight against the road.
However, Lancaster City Council leader Coun Eileen Blamire said: “That vote was taken at the very last minute, and was rushed through. We wanted the western bypass route, but we had to accept that it was the northern bypass route or nothing.
“The Morecambe Bay Independents also voted against it at the time.
“Personally, from the Labour group point of view, we support the road and are delighted that it’s happening.
“It will improve our tourism offer and help with traffic problems.”