Not only could your pet be injured, but so could you. Safety is very important in treating your dog. Therapy should not be done by a non-professional or someone not properly trained in hydrotherapy techniques. Bring your dog in for professional swim therapy. This is a common problem.
Pools are expensive to rent and maintain.
Swimming is good for your dog, but if you are trying to heal your dog, it takes much more than just swimming. The temperature must be right, you must protect yourself and your dog from further injury, and you need a working knowledge of cranio-sacral and MFR techniques in order to therapeutically help your dog. Bring your dog in for professional swim therapy. Not after surgery, spinal injury, stroke, or myelogram because your dog will probably get worse. We would not recommend swimming any injured pet in a non-controlled environment.