Here are some photos of Topanga canyon creek on the coastal side where there is no air that is basically full of carbon particulate because there is no air basin full of cars. In 2001 Cold Springs creek in Santa Barbara had no frogs but Topanga was full of frogs, and of course lots of healthy green algae.
Massive amounts of algae were present even in 2003 even though there was less than 2001. Note the dried algae hanging from the rocks.. Cold Springs creek in Santa Barbara showed this condition years ago.
Cold Springs creek actually had more algaes than this in the mid 1980's. Thick, dark green pads mounding over the water level were present in every pool with sunshine. Cold springs is steeper and flows faster and so had more oxygen mixing in.