Guanabara Bay, Brazil (CNN) When Victoria Jurczok and Anika Lorenz rip through the water aboard their racing skiff, they are doing far more than sailing at the fastest possible speed.

The two athletes from the German Olympic Sailing team are also learning the unique currents, tides and wind patterns of Rio De Janeiro's Guanabara Bay, to try to get an edge when they compete in the upcoming Olympic Games.

And they are keeping a look-out for floating obstacles.

"Its possible you hit while sailing some plastic or you don't know what," says Jurczok, a 26-year old from Berlin. "It can either damage the boat or slow you down."

"We hit a lot of plastic bags," says Lorenz.

"But our training partners also hit a chair," she added.

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Floating debris

On the surface, the view of the Guanabara Bay and the iconic Rio skyline of soaring mountains and peaks is unparalleled. But look closely, and you can find long garbage trails of debris flowing through the areas where Olympic teams are training before the games.

The flotsam includes chunks of wood, rubber sandals, sneakers, and of course, plastic bags.

But this isn't the kind of pollution that the athletes are worried about.

One of Jurczok and Lorenz's teammates had to have emergency surgery after a race in Rio last summer, when small cuts on his legs became horribly infected.

Dumping ground for waste

For all its beauty, the sea here has also been a dumping ground of raw sewage washing down out of the Olympic host city. The horribly polluted waters are an environmental hazard that the city has struggled with for decades.

Brazilian authorities insist the bay will be safe for the sailors.

Eduardo Paes, the mayor of Rio, told CNN that the Games will be held during the time of year when there is less rain, and thus less effluent pouring into the sea.

He spoke to CNN last week at the launch of a brand new sewage treatment plant. It would provide several hundred thousand residents of Rio with modern treatment of their waste for the very first time.

A new sewage treatment opened last week will provide services to several hundred thousand Rio residents.

But there are many, many more Brazilians living in the surrounding metropolitan area, who do not have sewage treatment.

"The twelve cities that are around Guanabara and the state level have missed the opportunity to solve a problem," Paes conceded.

The worst of the pollution is immediately noticeable at points where urban canals spill out into the bay.

At one such location, the air is thick and toxic with the stench of raw sewage. Dark black clumps of debris float on the water's surface.

Fisherman Filipe Fernandes has to slow down his small motorboat to protect the propeller from all the garbage floating in the water. Still, it doesn't take long before a plastic bag snarls and stalls the propeller.

"It's impossible to swim here," Fernandes says, after he uses a long metal hook to rip the plastic bag off his propeller. "You'll get all sorts of sicknesses. Skin diseases. Hepatitis. And of course you can't fish here."

Another fisherman named Reinaldo Coelho moors his boat here in the Fundao Canal, a stone's throw from where grey liquid spills out of a large concrete pipe directly into the water.

"It comes from the houses," Coelho says. "There is no basic sewage. Look at Rio now, we are going to have the Olympics, but we don't have a basic sewage system. There's no logic."

Signs of improvement

According to a May 26 statement by World Sailing, the governing body for the sport, the water quality is "noticeably better" in launch areas around one of Rio's main marinas.

"The trend lines are encouraging," announced the group's CEO Andy Hunt, after holding meetings with city officials and environmental experts. "But it will be important that not a single day is lost in implementing the remaining measures that are planned, including the installation of a series of new eco barriers."

The two German sailors Jurczok and Lorenz say they try not to focus on the water pollution.

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They will both be competing for the first time in the Olympics in August. It will also be the first time women will compete in the 49er FX class of sailboat.

When they catch a strong gust of wind, the two sailors hike their bodies out over the water, attached to the mast of their 49er FX by long harnesses fixed to their waists. At these moments, the light-weight craft almost looks like a two-person windsurfer.

Their team has medical doctors on stand-by in the event of any complications due to the water.

As far as other precautions go, they say they try to avoid swimming and try to keep the water from getting into their mouths.

After each training day, Lorenz says, "we wash all our neoprene clothes in special washing liquid, so we can ensure that all the bacteria is out."