Hi sidevalve,
The video you posted of the River Bidassoa in spate is a reminder that - unlike the benign, knee-deep conditions many of us experienced during last September's commemorative walk - a crossing in December in the early hours after a 5-hour night-trek across the foothills of the Pyrenees would have been tricky and unpredictable.
Add to that the requirement not to use torches and one can get some idea of the degrees of difficulty and danger involved.