"Cliff Hanger the Rain, and the River" is a book in The Adventures of Cliff Hanger series by Livingston Dangerously. This one was meant to teach the remarkable letter "R".
Cliff is, as usual, hanging from the cliff, when it starts to rain. Thus, a river forms under the cliff. He reaches for his survival manual and learns that if there's a rapidly rising river underneath your cliff, jump into it, and reach out, grab a salmon, and let it pull you to safety. Cliff is lucky it doesn't require a salmon suit, as he rented his to a guy a few years ago, and he never returned it. Cliff rams into the river a sees a salmon. He grabs onto it, but it turns out to be the guy he lent his salmon suit to. Cliff then goes off a rapidly raging waterfall, and is ran back to the cliff.