algae in ponds and rivers isn't a problem because the water is always changing over. Technically, pool water is stagnant water and you don't want to swim in THAT!

Every person who enters a pool brings all sorts of contaminants with them, including a small amount of fecal matter, as well as other bodily fluids. The diseases that are waterborne are pretty dangerous and disgusting. Chlorine kills them all.

Then there's birds pooping in the water (had that in late May) bugs, dead animals and other organic matter rotting in the water....

But if algae is growing, either you have no chlorine or it's being used up killing the algae..and you have no protection against viral, bacteria and fungal infections.

If you swim in algae-filled pools and haven't gotten ill, you are lucky.

Carl