Is Oregon lake extremely pure water? If so, why?
The visibility or "clearness" is more a matter of suspended particulates, and organic material such as algae, than of dissolved material.  For instance, runoff from glacial streams can be nearly opaque due to suspended rock flour, yet "pure" in the common sense of not having much in the way of algae &amp;c. Conversely, some parts of the oceans can be very transparent due to lack of suspended sediment &amp; organic matter, yet still have the same dissolved salts as other parts of the ocean.