Why did Rio's Olympic diving pool turn green overnight?

The pool was blue, and now it's green. NO ONE KNOWS WHY.

There are two pools in Rio for the Olympics. Yesterday, both of them were clear and blue. Today, one of them is green.

Uhh, the diving pool's not supposed to be green-ish, is it? (Photo via @mattmajendie): pic.twitter.com/1wZgjajD4g

- SB Nation (@SBNation) August 9, 2016

OK, the pool's green. That's fine. Surely there's a good reason for it ... right? Riiiiight?

The water quality at the Maria Lenk Aquatics Centre was tested and there were no risks for the athletes. We are investigating the cause.

- Rio 2016 (@Rio2016_en) August 9, 2016

"The diving pool has turned green and no one knows why." Good #Rio2016 quote at the media center.

- Andrew Sharp (@andrewsharp) August 9, 2016

Seriously, this pool is VERY green and we aren't sure why.

Something unfortunate has happened at the Olympics diving venue https://t.co/NSQRtVvTZx pic.twitter.com/eo8yQSVO6w

- Timothy Burke (@bubbaprog) August 9, 2016

Like, REALLY FREAKING GREEN.

Photo by Adam Pretty/Getty Images

I'm told by swimming pool connoisseur and SB Nation coworker Seth Rosenthal that green pools usually happen because there's too much algae and not enough chlorine. The pool is covered but not completely indoors, so it is possible for that algae to sneak in and break out there overnight.

From the website pooluniversity.org, which certainly seems like it might be a good source. It also says that if it is algae, it's not harmful to swimmers, so that's good.

Algae spores may get into the pool through rain, wind, or contaminated equipment and swimsuits. When the swimming pool conditions are not well balanced, an algae bloom can occur overnight. These pool conditions include an improper imbalance of water chemicals, presence of nitrates and or carbon dioxide, warm temperatures and sunlight. Of course, poor circulation, filtration and sanitation are always the main cause of the algae. Algae blocks filter pores causing a decrease in the filter effectiveness which may require you to do more backwashing. It consumes chlorine in the water that should be used on other contaminants creating a higher chlorine demand in the water. Algae itself does not harm swimmers but if a pool has algae, it may be a haven for pathogens like E-coli bacteria. Although algae do not harm swimmers, no one wants to go swimming in a pool that is full of algae.

So the end result is this: We have no clue why the pool is green. It definitely should be blue, like most pools. WELCOME TO RIO 2016.

Please respond if you have better explanations for this green pool.