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

[31j20b3]

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?

[Lochloosa]

1. Its basically a tidal basin Potomac brackish water

[31j20b3]

3. Well that's an answer that accounts for what was seen

Potomac water is eutrophic. That means rich in nutrients.

Put baby algae in a bath of warm nutrient rich water and you unsurprisingly get a huge algal bloom.

I hope the NPS doesn't attempt to use silver carp (which do feed on algae) as a control Or we will have fish jumping out of the pool and assaulting visitors to DC (just kidding, well sort of)

[Ocelot II]

2. Both the tidal basin and city water. Here's a really good explanation of how the whole system works,

and why there are still problems with it.

Water is pumped from the Tidal Basin, an inlet of the Potomac River, to the treatment plant. There it is filtered and purified before being fed into the Reflecting Pool.

But when the water from the Tidal Basin is too murky or filled with algae — which is often — the pool is filled with city drinking water instead. This happens especially in the hot summer months, when algae blooms are prevalent.

No matter where the water comes from — the Tidal Basin or the city — it does not stay clean for long. In warm weather, the shallow pool bakes in the sun.

The treatment plant is supposed to combat this problem, using screens and sand to filter the water and a system that infuses the water with ozone gas, which kills algae and bacteria.

But it doesn't, because of all the leakage in the plumbing. The system can't keep up with the water loss. https://www.nytimes.com/interactive/2026/05/31/us/trump-reflecting-pool-problems.html?unlocked_article_code=1.qVA.Hbdd.gbkvbjqGoMdC&smid=url-share

[31j20b3]

5. Filtration wouldn't rid the water of nutrients it would require biological consumption

that's done in primitive water treatment by moving the raw water over rocks that have algae growing on them. It's done in tertiary systems by microorgansisms that under aerobic conditions consume the nutrients.

[Goonch]

4. ;-{) Water is pumped from the Tidal Basin, an inlet of the Potomac River, to the treatment plant.......

Water is pumped from the Tidal Basin, an inlet of the Potomac River, to the treatment plant. There it is filtered and purified before being fed into the Reflecting Pool.
An illustration showing how water is pumped in from the Tidal Basin into the water treatment plant, where it is then moved into the Lincoln Memorial Reflecting Pool.
https://www.nytimes.com/interactive/2026/05/31/us/trump-reflecting-pool-problems.html

[Jerry2144]

6. With all the water fowl

There’s a bunch of duckshirt and gooseshirt adding nutrients, too. That helps the algae bloom.

If you add in all the GOP batshirt, chickenshirts, horseshirt, bullshirt, and dogshirt coming from them and their policies, that algae is living the good life in a nice hot tub.

[pat_k]

7. And of course, painting it a dark color added heat.

A bonus from the algae's perspective.
https://www.yahoo.com/news/us/articles/american-flag-blue-pipes-4-133546018.html

The timing—just days after the pool was refilled—has prompted debate over whether the darker coating could be playing a role.

Darker surfaces absorb more sunlight and heat than lighter ones, which in shallow water can raise temperatures and increase the energy available for algae growth—potentially accelerating reproduction rates.

Lowe said this effect could be significant, as darker surfaces effectively act as a heat source. "The darker an object the more light it absorbs and the warmer it gets," he said, adding that this can create "perfect conditions for algae to bloom" in shallow, sunlit water.