Algae

[orthoclad]

15. This is river water

recently enriched with massive sewer spills. Probly flushed by now, but you get the point.

Who needs birds etc. to introduce algae when it's urban river water, rich in nutrients and floating cells? The higher temps from the paint can speed reproduction, but I'd say the main limiting factor is the available nutrients - which is why Chesapeake Bay folks want nitrogen and phosphorous reduced in river water.

It's not a swimming pool, it's an ecosystem rich in primary production (algae), which is missing it's grazers. Add snails and aquatic insects. The flying species will find it soon, but obligate aquatics will need to be introduced - maybe by duck feet : ) .