In 1992, a cargo of 29,000 plastic (not rubber) ducks, turtles, and frogs was swept overboard from a container ship. The ship was bound for Seattle, carrying a cargo of toys manufactured in China. When the toys' containers fell overboard, they broke open, releasing the toys to the ocean currents. Since their voyage began in 1992, the ducks have been floating around the world's oceans, turning up on beaches across the globe.
Retired Oceanographer Dr. Curtis Ebbesmeyer has been tracking the toys on their journey and predicting their future path using ocean current models. (Ebbesmeyer studies all sorts of floating stuff, calling his science "flotsametrics.") According to Ebbesmeyer's predictions, the toys will start washing up on British beaches soon. If you find one of these ducks on the beach, check for two identifying characteristics: it should be bleached white by the sun, and it will bear the manufacturer's name: "The First Years." There are many references online to a $100 reward for returned ducks, but links to the reward page no longer work.
You can read more about the toys' journey in recent U.K. coverage: The Daily Mail, BBC News, and The Times Online. Also of interest: a list of resources related to the duckies, Ebbesmeyer's page on the duckies, and a 2003 NPR interview with Ebbesmeyer.