We got a shock 2 weeks ago when the color of the water in the swimming pool at our condo turned into green - like polluted sea water. Surprisingly, some residents still jumped in to swim, how gross. However, the pool was later cordoned off and closed for swimming for about a week. When the pool specialists came to fix the problem, the water turned blue again.... slowly. Here's a picture of the pool with 2 colors - green is the part that is not cleaned yet and blue is the part that is already cleaned. Amazing!
Picture taken from the 5th floor of our unit.