Here's where you can click to see water quality measurements in your part of the U.S. The site was set up by the U.S. Geological sruvey. It gives real time data on turbidity, pH and temperature among other measurements. This comes from active monitoring stations around the U.S. Mostly in highly populated areas.
I notice for most measurements areas like Phoenix, Arizona, and northeastern Montana there is no data. Meanwhile there are numerous stations on federally owned land and along the coasts as well as around the Great Lakes.
The USGS sees this data as being used for eberything from flood warnings to decisions about which day is good for water-skiing or fishing.