The Official Rules of Golf appear on the About.com Golf site courtesy of the USGA, are used with permission, and may not be reprinted without the permission of the USGA.

Except when both the loose impediment and the ball lie in or touch the same hazard, any loose impediment may be removed without penalty.

If the ball lies anywhere other than on the putting green and the removal of a loose impediment by the player causes the ball to move, Rule 18-2a applies.

On the putting green, if the ball or ball-marker moves in the process of the player removing any loose impediment, the ball or ball-marker must be replaced. There is no penalty provided the movement of the ball or ball-marker is directly attributable to the removal of the loose impediment.

Otherwise, if the player causes the ball to move, he incurs a penalty of one stroke under Rule 18-2a. When a ball is in motion, a loose impediment that might influence the movement of the ball must not be removed.

Note: If the ball lies in a hazard, the player must not touch or move any loose impediment lying in or touching the same hazard — see Rule 13-4c.

PENALTY FOR BREACH OF RULE:
Match play — Loss of hole; Stroke play — Two strokes.

(Searching for ball in hazard — see Rule 12-1.)

(Touching line of putt — see Rule 16-1a.)

©USGA, used with permission