Water polo players complained chlorine was stinging their eyes after a second Olympic pool turned green and officials pumped in chemicals to fix the problem.

Tony Azvedo said he could hardly open his eyes for the last quarter of the US match with France as organizers rushed to turn the water back to blue.

After the diving pool suddenly turned from blue to green because the cleaning system ran out of chemicals, the water polo pool followed suit.

"What's ridiculous is not the green water. I've played in plenty of pools with green water. The problem is they put way too much chlorine in. I could barely open my eyes for the final quarter," Azvedo said on Wednesday.

"Who cares about the green water? The water could be any color, it doesn't matter. What matters is that it's safe for us. This is the Olympic Games and they are putting so much chlorine in the water that people can't see. You can't have that."

FINA, the international swimming federation, said "the reason for the unusual water color ... is that the water tanks ran out some of the chemicals used in the water treatment process. As a result the pH level of the water was outside the usual range, causing the discoloration."

Organizers stressed there was "absolutely no risk" to athletes and said the water should return to normal on Thursday as the chemical treatment continues.

"As a matter of fact, we could have improved the water much faster using chemicals and we're not doing so in order to respect the fact that we cannot have any risk whatsoever to the health of the athletes," said spokesman Mario Andrada.

Hungary's Gergo Zalanki also complained about the water on Wednesday.

"My eyes hurt from the water, it's not good. It feels like they added more chlorine to the water but I'm not sure," he said.

"I'm used to it because we have a lot of water like this in Hungary, but I think there might be something else wrong too."