Some places do not look dangerous at all but in reality, they are completely opposite. Take an example of the Potomac River that is absolutely not safe for swimming. It is because it has rapids that can easily pull you under and you’ll find yourself at the bottom within no time. Once you are pulled by the rapids, it would be hard for you to come to the surface. Given that humans can’t swim underwater (unless you are a superhuman), it is best to avoid this place.