Roads around the 2012 Olympic rowing venue in Eton will not cope with 30,000 expected spectators causing gridlock, a councillor has said.
Colin Rayner, of Royal Borough of Windsor and Maidenhead, said nearby Windsor Castle and Legoland, plus rush-hour traffic, would add to the chaos.
The Olympic Delivery Authority said plans included temporary park-and-rides and shuttle buses from rail stations.
It also said it was planning pedestrian, cycle and ferry access.
Mr Rayner said he had concerns about the plan for a single road access route to the site via Windsor Racecourse.
He said: "We're really excited about having the Olympics.
"But what we want to do is make sure we work with the Olympic Delivery Authority to make sure we can get 30,000 people in and out without Windsor ceasing to function, and Maidenhead ceasing to function, and Slough.
"What we want to do is bring our local knowledge to the Olympic Delivery Authority so it understands how Windsor and Maidenhead works.
"Also, what we want to do is make sure all the hotels in Windsor, Slough and Bracknell all benefit from this."
He said the athletes and the "Olympic family" would go in the main entrance of Dorney Lake, which amounted to about 5,000 people.
But the other 25,000 would have to go via Windsor Racecourse.
An Olympic Delivery Authority (ODA) spokesman said: "We are looking to make the best use of all transport modes for Dorney Lake.
"Detailed discussions on these plans are currently taking place with a number of landowners and we expect to be able to confirm details early next year.
"We will continue to work closely with local authorities as we develop these plans."