Campaigners fighting plans for the project on their doorstep have posted a video on YouTube in the latest stage of their fight.
They say recent flooding near the site at Bathampton Meadows should halt the scheme in its tracks.
But Bath and North East Somerset Council says the risk of flooding at the Meadows itself is less than one in 1,000 in any one year.
Members of the Save the Bathampton Meadows group watched in horror as last week's snow melt and torrential rain caused floodwater to lap at the edge of the field earmarked for the 1,400-car facility and saturated a flood plain created to protect Bath whenever the Avon bursts its banks.
They have now placed footage of the flooding on the website as part of their campaign to prove the facility is at risk of flooding, is an outdated method of cutting congestion and will destroy the approach to Bath.
The park and ride on Bathampton Meadows, next to Mill Lane and near the A4 Batheaston bypass, is a key part of a £60 million package of transport improvements planned for Bath.
The council has submitted four planning applications in a bid to get the package passed. The deadline for public objections is March 6, and hundreds of comments have alreay been made on the various elements.
The package hinges on approval for the creation of the new A4 Eastern park and ride, expansion of the existing Odd Down, Lansdown and Newbridge sites and a controversial Bus Rapid Transit system linking Newbridge park and ride to the city centre.
Council cabinet member for transport Cllr Charles Gerrish (Con, Keynsham North) said: “There is an extremely low risk of flooding to the site, according to independent experts who have used data from the Environment Agency. The data suggests the likelihood of an extreme flood on the site is less than 1 in 1,000 in any one year.
"Bath and North East Somerset Council has carefully designed the site to minimise any flood risk.”
Its environmental statement says the development will incorporate a full sustainable drainage system, including porous car parking spaces and a wetland area as part of the landscape enhancements proposed.
"The drainage system will allow water to drain through the car park at a controlled rate which is consistent with current conditions."
But Batheaston resident and pressure group spokeswoman Alison Millar said she hoped the video and photographs would ring alarm bells for the authority.
She said: "These photos clearly show the water breaching the boundary of the site. The council may argue floods like this only occur every 200 or 1,000 years but with global warming and the recent extreme weather there is just no guarantee of that. They may as well call it a 'park and swim'.
"The council says they will be putting measures in place to prevent it, but I fail to see how they can stop petrol and oil from the park and ride surface running into the River Avon and polluting it.
"It is just too close to the flood plain for comfort, and that flood plain has been under water three times in the last year, not to mention the visual impact it will have on the villages surrounding and looking down onto it.
"Surely mucking around with that flood plain will have an impact on the whole city and its protection from flooding?"
The council has submitted five flood risk assessments carried out by various contractors alongside its application.
The YouTube footage is at http://www.youtube.com/watch?v=hnlTXCPgVss