West Dunbartonshire Council will formally object to plans for a £30m holiday resort in Balloch.
In a show of cross-party solidarity, councillors unanimously agreed to oppose the controversial proposals.
The local authority is a statutory consultee and will send its formal response to Loch Lomond and the Trossachs National Park, who are due to consider the application in principle.
The plans have been lodged by theme park operator Flamingo Land and Scottish Enterprise.
The complex would include a variety of family accommodation facilities, including a 60-bedroom apart-hotel, 32-bedroom budget accommodation, 131 self-catering units, six private houses and 15 apartments.
It would also be home to a boathouse, leisure centre and restaurants.
Around 56,000 people have signed an online petition, led by Ross Greer, of the Scottish Greens, against the large-scale development.
Officers had earlier put together a draft response highlighting what they believed were the benefits and drawbacks of the application.
They said it would be a huge boost to the economy but could exacerbate traffic problems.
But councillors tore it up with members across the SNP, Labour, Conservative and Community Party adding their contributions.
