The pump still works, but something’s broken.
Some busted pipe under tons of concrete.

Without that one little tube, nigh impossible to get at and fix, the system failed
And you stopped being a swimming pool.

But a pool you remained,
as water shifted from blue to green,
clear to cloudy, vacant to crowded.

Chlorine and chemicals thinned by rain, absorbed by leaves,
perhaps imbibed with gusto by some intrepid microorganisms like moonshine-drunk prospectors plowing into an unexploited region.
You became habitable, then vulnerable, then welcoming, then home.

In time, enough brazen algae and audacious critters crawled into you,
and did those creeping, growing, icky life things
that you went from a sanitary refuge for overheated children to
a strange captive ecosystem, bound by four concrete walls, a deep floor, and a few clogged pipes.

A palette of greens: from sickly, puke pale to nearly bile-black.
A scent not of pond, but off; a smell from the uncanny valley.
A habitat for bacteria, paramecia, amoebae, and fucking mosquitoes but
Woe betide the snake or toad, or frog that tries to find refuge in you;
those walls are a lethal prison to wrong-size creatures,
And the accretion of thriving muck at the bottom hungers, always.

And yet, to others, to so much that spawns and blooms and perishes,
You are home; you are enough.
Their tiny lives pass, full, within your poured walls;
content to have served their purpose.
However unnatural their place, and unwelcome their habitation.
They get to live.  Because of you.