Rubber boots, fitted with a removable felt liner like snowmobile boots. They have a tie off collar at the top to keep snow,etc from dropping into the top of the boot. With a pair of woolen socks, they fit my foot just fine for a day of walking around taking pictures of swamps, ponds, and shallow watercourses.
First time that I had seen them. Found at Marks Work Warehouse, for about $40.
I wore these on the Brits and Yanks workshop about a month ago, and were they ever useful; my trusty old hiking boots (wedding gift from my wife 12 years ago along with a $70 gold band in lieu of an expensive ring that I would never wear anyway) only saw service on the first day, then it was rubber boots for almost every other outing.