The River / Slow down write

I was on a hike with my sister and dad beside a really fast flowing creak. We were right beside a bank that led straight down to the creak. I was just about to say what would.... Then the ground broke and I slowly fell into the crisp cool water. I hit with a splash and herd a loud crack. I thought did I hit a rock or a log or brake a bone. I was waiting for the searing pain. It didn't come. I waited. Then I slowly got out of the river and back onto land. I never found out what made the loud crack.