Water Hazard

From the official rules of golf:

Water Hazard: A "water hazard" is any sea, lake, pond, river, ditch, surface drainage ditch or other open water course (whether or not containing water) and anything of a similar nature on the course.

All ground or water within the margin of a water hazard is part of the water hazard. The margin of a water hazard extends vertically upward and downward. Stakes and lines defining the margins of water hazards are in the hazards. Such stakes are obstructions. A ball is in a water hazard when it lies in or any part of it touches the water hazard.

Note 1: Stakes or lines used to define a water hazard must be yellow. When both stakes and lines are used to define water hazards, the stakes identify the hazard and the lines define the hazard margin.

Note 2: The Committee may make a Local Rule prohibiting play from an environmentally-sensitive area defined as a water hazard.