It still happens in the US.

Chlorine breaks down when exposed to oxygen and light (note it’s a clear tank).

My unit at home has a clear tank that’s inside the unit - it builds up a slick layer of something, so I wash it weekly.

Edit: chlorine is also not effective against everything. Having managed outdoor pools, algae can be pretty indifferent to chlorine levels. If a pool gets an algal bloom, chlorine won’t stop it - you need heavy filtration to mechanically remove it.