Festival-goer Ayden McNamara said he had been waiting to board a ferry at Portsmouth for three hours before finally being able to board.
Video by @BrainzUK via Twitter of traffic backed up at Wightlink's Fishbourne terminal.
Southern Vectis was asked by police to suspend network services temporarily, while resources were dedicated to dealing with school pick-ups.
A revised network service was re-introduced at around 4.15pm. The Isle of Wight Council said school transport had been affected and asked students and parents to be patient.
At around 6.15pm Southern Vectis said it was unable to operate its Route 4 service, from East Cowes to Ryde, or Route 5 service, from East Cowes to Newport, because of heavy traffic in East Cowes.
Earlier it advised customers who wanted to travel to Newport from Ryde to use the route 2 or 8. due to severe delays on routes 4, 5, 9, 25 and 37.
At 2.10pm Southern Vectis said on its Facebook page: "Route 5: Severely delayed, up to 4 hours journey time. Passengers to and from East Cowes and Newport please use route 1 and the floating bridge."
Traffic congestion at the Whiterails Road, Briddlesford Road roundabout. Picture by Gemma Barrett.
Route 1 buses have also experienced problems according to the Southern Vectis Facebook page at 1.19pm: "Some journeys are being lost due to impact of other delays on drivers' legal driving hours.
The company said the Ryde to Newport route was suffering the worst delays: " Route 9: Severely delayed - it is now taking 5 hours + to do one return journey."
Bus routes 4, 5, 9 and 25 were severly delayed with route 9 journeys taking up to two and a half hours according to the Southern Vectis Facebook page at 12.09pm.
They said: "Please bear with us, we are doing the best we can, but these delays will have an impact on our drivers' legal driving hours. The worst affected area is the Ryde - Wootton corridor. All route 5, 9 and 25 are on diversion out of Newport via Staplers.
"Please allow plenty of time for your journey today."
Hampshire Constabulary posted on their Facebook page at 12.29pm: "Tracks are in place across muddy ground for motorists to reach an extra car park at the IOW Festival.
"Police motorcyclists are on patrol between Fishbourne, Whippingham, Wootton Bridge and Newport to help manage the flow of traffic onto the site as swiftly and safely as possible. We are working closely with the organisers, ferry companies and other emergency services."
At 11.43am traffic was taking an hour and thirty minutes to get from Newport to Wootton and over two hours to travel from Ryde to Wootton according to Southern Vectis on Twitter.
However @FestivalCop, an official Hampshire and Isle of Wight Police festival twitter feed, said at 11.46am: "Good news folks, a new car park opening shortly which will free up the congestion. Bear with us, team working hard on it now."
At 11.02am Southern Vectis reported on Twitter: "Fishbourne, Wootton, East Cowes and Fairlee Road traffic has been at a standstill for over an hour."
It is understood this was caused by vehicles intending to enter the camp site for the Isle of Wight Festival on Whippingham Road.
Festival organiser John Giddings apologised on Twitter for the problems, which he said were partly due to delays in people parking at the site.
Red Funnel and Hovertravel services were running to schedule, although Red Funnel said there were traffic delays around East Cowes.
The festival kicks off tonight with sets from acts including Primal Scream and the Stranglers.
Around 70,000 people are expected at the site over the weekend, with headline acts including Pearl Jam, Tom Petty and Bruce Springsteen.
At 9.59am bus routes 4, 5, 9, 25 and 37 were all subject to long delays due to the festival traffic, according to Southern Vectis.
At 8.35am Fairlee Road was gridlocked according to Southern Vectis, which said it was running all route 9 buses via Staplers due to the delays.
At 7.50am it advised all customers travelling from East Cowes to go across to Cowes to use the route 1 service instead.
Traffic coming from Ryde was backed up to The Sloop in Wootton according to @lisylou via Twitter at 8.48am.
There are a number of road closures in place due to the festival, to see which road are affected, click here.