From the Rules Forum: Hazard(ous) Drop Ruling

Have a question about the rules of golf? Post it to our Rules Forum where experts and fellow golfers will jump in with answers. For example, here's a question recently posted:

I hit my ball into a lateral hazard, got a new ball from my bag and dropped it near the point of entry. The ground was so steep that the ball I dropped began rolling into the lake.

Seeing that I was going to lose my brand new ball without ever hitting it, I naturally stopped it from rolling with my foot.

This was a casual round with friends, so I just picked up the ball and dropped it again. This time it didn't roll, so I played on.

Had this been a tournament or competition of some kind, I would have given the situation more thought. What is the official rule for losing a dropped ball into a lake? I assume you're not expected to take another stroke penalty, but what about the ball? Are you supposed to just stand there and watch it roll into the lake? I'm an amateur and have to pay for my golf balls!

What's the ruling?