The R&A - Working for Golf

Loose Impediments

You may move a loose impediment (i.e. natural loose objects such as stones, detached leaves and twigs) unless the loose impediment and your ball are in the same hazard (i.e. bunker or water hazard). If you remove a loose impediment and this causes your ball to move, the ball must be replaced and (unless your ball was on the putting green) you incur a one-stroke penalty.

Loose Impediments