Rachel Fattal of the United States is surrounded by Hungarians as she takes a shot in a water polo game Saturday. The Americans won, 11-6, and after the game, Rio organizers announced plans to drain the water polo pool. (Rob Carr/Getty Images)

The improper dumping of 80 liters of hydrogen peroxide into two competition pools at the Rio de Janeiro Olympics — the diving well and adjacent pool for water polo and synchronized swimming — is the cause of the water’s unnatural green color, said Mario Andrada, chief spokesman for Rio 2016.

Andrada unveiled two fixes during an hour-long news conference Saturday at Maria Lenk Aquatics Centre.

• All 3.725 million liters of oddly bluish-green water is being drained from the larger pool and will be replaced by water pumped in from one of the adjacent practice pools that wasn’t treated with hydrogen peroxide. The process, which should take 10 hours, is necessary because the pool hosts synchronized swimming beginning Sunday. Those competitors must be able to see one another under water, and judges must have a clear view in order to assess their performance.

• Water in the diving well, which reached a more jarring shade of green than its neighbor, will not be drained. Rio organizers, in conjunction with advisors from FINA, swimming’s international governing body, and the International Olympic Committee, believe the green water — and the proliferation of algae that they believe caused it — can be remedied by a change in the pool filters. And time.

The material inside the filters was changed Friday night, Rio officials said. By Saturday afternoon, the water appeared more greenish-brown than green. Andrada suggested that the algae that had presumably bloomed because of the ill-advised mix of chlorine and hydrogen peroxide was dying off.

The Aug. 10 photo shows the water of the diving pool, right, and water polo pool, left. Although the diving pool is greener, officials are changing water in the water polo pool so it can accommodate the synchronized swimming competition. / (Matt Dunham/AP)

Olympic divers had voiced concern about the water, and water polo players complained that their eyes burned. Over the past few days, Andrada has offered different explanations — heat, lack of wind, over-use, a change in alkalinity and too much agitation.

Gustavo Nascimento, the venue director for the Games who joined Andrada at Saturday’s news conference, fielded most of the technical questions, but made clear at the outset that he was not a chemist or a medical professional.

Andrada said that hydrogen peroxide, which is a clear chemical compound, is a legitimate solution for cleaning pools. But, he noted, it should not be used in conjunction with chlorine because it negates chlorine’s ability to kill off organic matter.

That, officials believe, is where the problem started. Andrada said that the hydrogen peroxide was added — 80 liters in each of the two pools — by a contractor on Aug. 5. The following Tuesday, the diving pool turned green and the larger water polo pool turned teal.

Andrada would not identify the contractor who added the hydrogen peroxide or disclose whether the contractor would face any financial penalty. And he reiterated the earlier assurance that no athletes’ health had been compromised, saying: “There was never a health risk, a health worry or concern in any shape or form.”

Andrada voiced regret that he had “over-promised and under-delivered” on the matter of the pools’ discoloration. “We should and could have done better in fixing it quickly,” Andrada said. “We learned a painful lesson the hard way.”

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Asked what would happen if the change in filters did not remedy conditions in the diving pool, Andrada said officials would consider revising the competition schedule — presumably delaying events — until it was fixed.

Shortly before the news conference, the defending Olympic champion U.S. women’s water polo team routed No. 2 seed Hungary, 11-6, to finish pool play undefeated.

U.S. team captain Maggie Steffens, who scored a game-high six goals in the physical contest, downplayed concern about the discoloration.

“At the end of the day, yes, the color of the pool may be different — pH levels, whatever it is,” Steffens said. “But it’s a pool, and if you’re a competitor like we all are — if you’re here for the right reason — you’re not worried about that.”

Said veteran Coach Adam Krikorian: “We’ll play in anything right now. I mean, you could put mud out there, and we’ll play in it.”