Chlorine does not make your dog sick. But you have to maintain a relatively low level of it in your swimming pool. As mentioned, you need to ensure that your pool is clean.  Everyone, including adults, ingests small amounts of chlorine when they swim, but dogs can swallow more. Thus, making it more dangerous for them. That's because they can't support themselves in the pool, unlike humans.  You need to supervise your dogs and ensure that they don't ingest a lot of water to avoid health problems. In addition, chlorine may also irritate your dog's skin. So you have to properly rinse them after swimming. And check for any signs of skin irritation.