The 500 Pound Algae Adage

Have you heard this adage? One pound of phosphorus can produce from 300 to 500 pounds of algae. You probably have. It is much quoted in articles and during presentations when the "greening" of lakes is discussed. It means a pound of the nutrient phosphorus entering a lake (or river) from wastewater or stormwater runoff can promote growth of up to 500 pounds of "pea soup" algae. Not only have I heard this adage, I have repeated it to others - which led me to ask, where did it come from, and is it TRUE?