What is "poohsticks"

Poohsticks is a sport first mentioned in The House at Pooh Corner, a Winnie-the-Pooh book by A. A. Milne. It is a simple sport which may be played on any bridge over running water; each player drops a stick on the upstream side of a bridge and the one whose stick first appears on the downstream side is the winner. The annual World Poohsticks Championships have been held at Day's Lock on the River Thames in the UK since 1984.