If you're looking for a spot along the Colorado River where your dog(s) can splash around, check out the Lower Onion Creek put-in. The boat ramp is out near Castle Valley off of Highway 128, and has an area where dogs can swim that is typically pretty calm (unless the river is running high). This is an active boat ramp, so be sure to keep your dog under control, but there's a lot of room to spread out and enjoy

DO NOT let your dog swim in the river when it's running high during spring runoff (May-July). Dogs can easily be swept away from areas that are normally calm for swimming. For extra protection, have your dog wear a PFD. I personally recommend the Ruffwear Float Coat!