Scary.......had a slightly similar experience in the Dobson some years back. Was walking down the river close to the water and wandered over a wet looking area ....smooth river gravel with maybe a few mm's water on the surface. Sank to almost to my knees immediately....lucky my big strong mate was a couple of metres away, and stepped over ( but not into the wet) grabbed my pack straps and heaved me forward. Still think back on that......
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