Rob Williams - Orangejack

I finally watched all 3 installments of The Lord of the Rings. We watched 1 and 2 Sunday and finished 3 last night. I liked it. I've seen 1 a couple of times and 2 once or twice. This time I really enjoyed all 3. I think I needed to watch them back to back to back to really enjoy them.

But I have a question. Why did the evil white wizard (whatever his name is -- the Count Dooku guy...names were confusing in the movies) lose his power? Seemed like a little flood washed out his little slave hole and he lost his power? I didn't get that.