Reminds me of the time when a group of us were backpacking in the Dolly Sods Wilderness in West Virginia. It had rained heavily over the past few days and our trail was flowing with runoff from the long storm. Proper trail etiquette is to hike on the trail, regardless of whether the trail is mud or water, dirt or rock, or whatever. If you walk on the berm, you will be crushing and flattening the soil on either side of the footpath and this will widen the trail leading to erosion. Simply, it may take ten minutes to clean the mud off your boots but several years for the sides of the trail to heal.