Dock jumping also known as dock diving is a dog sport in which dogs compete in jumping for distance or height from a dock into a body of water. There are dock jumping events in the United States and other countries such as United Kingdom, and Australia.
The jump distance is measured, by most organizations, from the lateral midpoint of the end of the dock to the point at which the base of the dog’s tail (where the tail meets the body) breaks the water’s surface. Purina's Incredible Diving Dog event measures the distance to the point that the dog's nose is at when its body enters the water. The jump distance is measured electronically using digital video freeze frame technology or, in some cases, is measured manually by judges.
Each team takes two jumps in round-robin format. The longer of the two jumps is that team's score for that competition. A jump in which the dog’s tail enters the water at a point further from the dock than another part of the dog’s body is scored using the point of the dog (for example, the head/nose) that breaks the surface of the water closest to the dock. If the dog’s strides are off so that the dog starts its jump before the end of the dock, that is a disadvantage, because the jump is always judged from the edge of the dock, not from where the dog leaves the dock. A jump is only official if or when the toy leaves the handler's hand. The dog is not required to retrieve the toy for the jump to count.
-- From Wikipedia