When I was a kid, the Potomac River was so dirty, if you fell in, they took you to the hospital for shots. Today, I drive over the same bridge that I did in my youth, and I routinely count a dozen or more people on stand up paddle boards.
This is the river near Violet's Lock. You can see clear to the bottom, and the fishing is excellent.
Behind this kayaker, you can see the impressive root structure holding an island in place. This is very near where Washington, D.C. takes in its drinking water, and every dozen years or so we get floods where the river here rises as much as 20 feet. If you're an island, you need help to hold on. Mother Nature, as always, obliges.