Motorists have been warned to expect delays of more than 55 minutes, with flooding having closed two lanes of the A82 in both directions.
After a day of torrential rain the second lanes on the flooded carriageway heading towards both Dumbarton and Glasgow have been closed, with congestion from the closure already leading to an increase in journey times.
Delays northbound and southbound are now estimated to be at least an hour, with pictures showing cars struggling to pass through deep floodwater on the approach to the Dunglass roundabout at Thompson's quarry.
Traffic Scotland are urging motorists to plan ahead and leave extra time for any journeys they need to take.
