Would a thousand of these fish be able to clean up the

[orthoclad]

10. Invasive species. They would colonize the Potomac,

which has more than enough invasive species already. Goldfish are pollution-tolerant; I've seen them in streams which won't support any other fish.

The Pool is filled with river water. I assume they filter it, using a mesh too coarse to filter algae cells, but which removes the native grazer species which keep the Potomac from looking like this. The solution would be to introduce native grazers like snails, insects, and algae-eating fish.

The blue color accelerates the growth, but it doesn't cause it. The algae are blooming because the river water they filled it with is loaded with nutrients like nitrogen and phosphorus. In an environment artificially free from grazers algae grows like crazy, until the rich soup of nutrients is depleted. Then they die, rot, and stink; the water loses the oxygen.

The Pool is like an oxbow lake filled with river water from a flood but with animals filtered out. It's an aquarium, an artificial ecosystem, not a swimming pool. Two very different things.

The vandal is Nature.

Aquarium keepers decades ago had the goal of the "balanced aquarium" (is that still a thing?), with just enough plants to provide oxygen and eat up the nutrients.

But the Feds are now a science-depleted ecosystem.