Residents give their views on the controversial larger ferries
Controversial larger ferries will continue between Hampshire and the Isle of Wight despite the High Court ruling they were unlawfully introduced.
A campaign group brought the legal challenge after Wightlink introduced three new ships on its Lymington to Yarmouth route in February 2009.
A judge declared the move was a breach of the European habitats directive.
Wightlink said the breach was not intentional and it had believed that it was acting in accordance with the law.
The Lymington River Association (LRA) argued that the bigger W class ferries created a greater wash and were damaging the Lymington River with its protected mudflats and salt marshes, which are rich in bird and marine life.
The historically low levels of marine risk on the river have not been eroded by the introduction of the W class ferries
It brought the legal challenge after Wightlink replaced its 35-year-old fleet with the new ferries as part of a £57m investment.
Mr Justice Owen, sitting in London, said Wightlink had failed to comply with its duties under the directive, which was initially "not fully and properly transposed into domestic law".
He said he recognised that, despite his ruling, the ferry service would continue to be operated with the new ferries, subject to certain measures.
But the LRA was justified in pursuing the legal action in order to clarify the law and the challenge was not an academic exercise.
In a statement, Wightlink said: "This breach was not intentional and, at the time of the decision, Wightlink believed it was acting fully in accordance with the applicable law.
"Wightlink notes the judgment, and will consider what steps it will be required to take in its role as competent authority to address this issue.
"Wightlink's new ferries continue to navigate the Lymington River and the historically low levels of marine risk on the river have not been eroded by the introduction of the W class ferries."
The company said that although no damage had been caused to the river, the firm was awaiting advice from Natural England before deciding on appropriate measures to ensure the area is not damaged in the future.
LRA solicitor Richard Buxton said: "This is a great judgment for the marshes and birds and other wildlife around Lymington and shows how useful European law is for properly balancing protection of the environment against commercial interests.
"It shows how our courts are able to help local people worried about the destruction of the environment they cherish in the face of a dithering government department and a big, intransigent company."