The origin of the rubber duck is not known, but its history is inevitably linked to the emergence of rubber manufacturing in the late 1800s. The earliest rubber ducks were made from harder rubber and lacked squeakers. The yellow rubber duck has achieved an iconic status in American pop culture and is often symbolically linked to bathing or bath tubs and bubbles and to babies and toddlers.
Jim Henson popularized rubber ducks in 1970, performing “Rubber Duckie” as Ernie, a popular Muppet from Sesame Street.
Some charities have run rubber duck races in which hundreds or thousands of rubber ducks are dumped into a river, pool, or other body of water and then floated down a race course marked off with buoys. The first one to float past the finish line is the winner. The rubber ducks are then retrieved and used again later. Due to environmental concerns, sites for duck races must be chosen with care.

There are hundreds of races held in the USA and internationally. The largest race in the United States benefits the Freestore Foodbank in Cincinnati, Ohio; over 100,000 ducks are raced to raise money for the organization.

One of the more famous rubber duck races is the Great Knoxville Rubber Duck Race. This race received attention when the Tennessee Supreme Court ruled that it was a lottery, which stopped the race for a few years. After the state amended its constitution to allow lotteries with special exceptions, the race was reinstituted.
A famous rubber duck race is the Halifax Duck Derby . This race has 10,000 rubber ducks in the Halifax Harbour along Bishops Landing. Theres a grand prize of 1 million dollars, Trip anywheres in Canada, Large Screen TV’s and more.

One other race was conducted in Australia in January 1988. It was run from the “High-level bridge” to the “Low-level bridge” near Katherine, New Territories on the Australia Day long weekend. Acting on behalf of the town’s Bicentennial Committee, Royal Australian Air Force officers Andrew Cairns and Jock MacGowan constructed the release cage from PVC pipe, purchased and numbered the ducks, printed tickets, and even arranged a helicopter flypast for the auspicious occasion.
On August 31, 2008, the Great British Duck Race was held near Hampton Court Palace, London. An estimated 250,000 blue plastic ducks were used.
Rubber ducks are used in small quantities as herding targets for radio controlled model yachts, the objective being to move all of the loose ducks into a floating pen.

Source