If you dive the Marine Room regularly, you already know the drill. Some mornings you wade in off the sand and can see clear across the flats. Other mornings you put your face in the water and can barely see your own hand. Same beach, same short walk from the car, completely different day. I get asked all the time whether the brown water is runoff, the tide, or the swell. At the Marine Room it is almost always the swell, and once you understand how it works you can tell what y