Ok, this is actually harder to get to then it seems. We got started and had a local guy show us the way for a tip we gladly paid.
The waterfall is absolutely amazing - the water is very comfortable and swimmable. The currents are a little strong, but manageable. There are a couple other falls higher up we did not go to, we were told they are smaller and less impressive.
Plan to spend a few hours from start to finish, and bring water shoes - the rocks are very slippery!
Do not miss this FREE (unless you want to tip a local guide to help you out) activity if you are in Montezuma!!