Waterloo biologist explains the science behind Rio’s green pools

Friday, August 12, 2016

Green olympic pool

The green water of Rio’s outdoor Olympic pools has baffled athletes, organizers and spectators but not Waterloo Biologist Kirsten Müller. She is fairly certain that algae is the culprit.

Although low chlorine levels, minerals and copper can also cause water to look green, it’s the cloudy appearance of the water that suggests the presence of an algal biomass.

The direct sunlight, warm weather and still water of the Rio’s outdoor pools are also the perfect conditions for algal growth. Since algae can reproduce very quickly, water can be clear one day and green the next. Which is what happened in Rio this week.

“People often don’t think about how algae impacts them,” says Müller. “Here we have something that aesthetically impacts the Olympics and gives a perception of poor water quality. These organisms are all around us and sometimes we have a hard time controlling them.”

Rio Olympic spokesman stated the green pool was the result of a decrease in alkalinity. Chlorine is used in pools to prevent algal and biological growth, but if the pool’s alkalinity isn’t correct then the effectiveness of chlorine decreases and the water isn’t being disinfected properly.

This is one of the issues with having an outdoor swimming pool,” says Müller, a Professor in the Department of Biology. “You have to do a lot more work to maintain the chemistry to ensure that there’s not going to be an algal bloom.”

The dramatic difference between the green diving pool and the adjacent blue water polo pool highlights how only a small difference in water chemistry is needed to tip the balance from clear water to a run-away algal bloom.

Rio’s pair of green pools

Algae gets around easily and quickly. Everyone was surprised to see that the clear, blue polo pool also turned green overnight.

Algae can come in from anywhere – air, rain or even the original water source,” says Müller. "You just need a splash of water or someone using the same pool equipment to transfer organisms from one pool to another.”

Officials test olympic pool water.

On Friday, the water in the hot tubs also had a green hue. That’s because of the water being transferred by the athletes’ body and swimsuits from the pool to the hot tub.

Algae are defined as a form of unicellular (or multicellular) plant or plant-like organism that lacks roots, stems or leaves; a common example includes seaweed. There are an estimated 40,000 different species of algae, with some lineages extending back more than a billion years.

“It’s hard to tell based purely on the pictures but my feeling is that it’s green algae, based on the bright grass-green colour,” says Müller.

Green algae are mostly harmless. Whereas cyanobacteria, the type of “algae” most often associated with swimming bans, has a distinct blue-green hue. Cyanobacteria are not actually an algae, but a photosynthetic bacteria that can secrete a range of irritating toxins.

Both organisms rapidly multiply under the right water conditions, dramatically changing the chemistry of the water.

From Rio to New York to home

New York City's Central ParkRapid algae growth in freshwater or marine water systems can lead to an algal bloom. These blooms occur in the presence of excess phosphorus or nitrogen. Depending on the amount of nutrients present, blooms in lakes and shorelines can persist for weeks or clear up in as little as 24 hours.

An algal bloom collapse can lead to anoxia, because as the algae cells die they decompose and remove all the oxygen in the water. The resulting hypoxic state ruins water quality, kills the fish and completely alters the ecosystem.

Already, there have been a number blooms in Florida and in the southern US this year. New York’s Central Park currently has a toxic algal, complete with a no-swim advisory.

“People don’t often think about how algae is actually going to impact them directly,” says Müller. “This is an issue pretty much everywhere right now because of all the hot weather we’re having. We’re likely to see blooms in Lake Erie and Ontario later this summer.”

According to Müller, the conditions this summer are perfect for a record number of blooms to appear: high temperatures, warmer waters and very few storms to stir waters and prevent them from getting super heated.

With temperatures getting warmer from climate change, it’s going to get worse and worse,” says Müller. “We’re now seeing algal blooms in Algonquin Park that were never there before.”

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