Just want to break this out as a question, what was the water source that filled the reflecting pool? [View all]

Algae are plants. To reproduce in the reflecting pool the progenitors of that green mass must be introduced to the water. This would not be much of a difficulty to the algae as algae are carried by virtually all water birds when they are wet from natural sources.

But as plants, algae also have nutrient requirements, nitrogen, phosphorus, potassium etc as memed in the phrase for freshmen bio students C HOPKNS CaFe Mg.

These nutrients are abundant, sometimes super-abundant in natural sources like the Potomac River, but they are generally controlled within tolerable limits in civic water supplies, especially things like living algal cells.

To produce what appears to be tonnes of algae, a rather large amount of plant supporting nutrients would be required to be present in the reflecting pool along with filterably large living algal cells to serve as a biotic origin of the descendant algae

Hence my question, Was the reflecting pool filled with a civil, treated and filtered water source, of more or less nutrient poor water or was it untreated water from the stone's throw away nutrient rich Potomac?