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Water Works

A six-step plan for fixing Rio

AFTER ROWING AND canoe sprint test events at Rio's Olympic venues earlier this year, several athletes blamed subsequent stomach and leg infections on their exposure to the highly polluted waters of the host city's Rodrigo de Freitas lagoon and Guanabara Bay. Here's how the water got so dirty, and how it might be cleaned in time for the Summer Games next year.

1Cut off the trash:

Every day, thousands of gallons of sewage and hundreds of tons of garbage flow into Rio's water system, including the lagoon and bay. The city promised to build eight new water-treatment facilities and cut this inflow by 80% ahead of Rio 2016, but it has built just one.

2Make a change:

A long-term solution will take years and lots of money, but there's a feasible short-term option that could make the Games safer for participants. It starts with moving the sailing events to the ocean and redirecting waste away from the lagoon.

3Patrol the shore:

The source of some of the bacteria and viruses may be animal sewage and decomposing wildlife, especially rats, but including pigs and horses. Local authorities could attempt to remove or cull these creatures in areas around the lagoon.

4Let it lie:

Toxic industrial pollutants, such as heavy metals, trapped in sediment do not biodegrade, and they are complicated and expensive to clean up. So for the time being those sediments should remain undisturbed.

5Feel the heat:

Stopping the supply of sewage flowing into the water will allow ultraviolet light from the sun to kill off the bacteria and viruses. Although this natural cleaning process takes time, it could do enough to make the water safe for competitors.

6Watch the sky:

One pitfall involves the weather. The Games are scheduled during Rio's dry season, but storms could wash pollution from streets into the lagoon, and rain and winds could stir the water and disturb the lake floor, recirculating pollution sediment to the surface.