I had a gelding I had to teach to do rivers with me. Make sure sure your horse has shoes on. NEVER ask a horse that is barefoot to walk on rocks like that.
Try to get a horse that has experience to help him cross. Do it together that way if anything happens you arent on your own. If your horse trusts you enough give it a go on your own, just make sure someone is always around tho.
The first time one of my old geldings gave it a go, I let him sniff, splash with a foot in the water for a few mins before asking him to actually cross. He crossed it with no issues. Keep your leg on, and let him have his head, he will take you to the other side safely you just need to let him-help you.