Apparently they are still in reasonably wide use around the world and in the U.S. Back in the '60s and '70s, the Engineering Experiment Station at the University of Tennessee, Knoxville, owned and operated a DUKW to carry on experiments on the Fort Loudon embayment of the Tennessee River in Knoxville. They kept it down in the parking lot of the boat ramp below Neyland Stadium. My father taught at UT and worked at the Experiment Station during that period and launched from that ramp so we used to watch it in action.
Bob