UPDATED: Olympic champion Nathan Outteridge and sick crewmate Iain Jensen have pulled off an extraordinary comeback to win a silver medal on a river of brown filth in Argentina.

The multiple world sailing champions and Rio Oympic favourites to defend their 49er skiff gold next year have fought their way back from outside the top 20 to win silver at the world 49er skiff championships.

It was a remarkable feat given Jensen was so sick he had to be taken out to the racecourse in a motor boat to sail each day and was unable to eat food for almost three days.

“After a very difficult and disappointing start to the week we caught it all back and go a silver medal so we couldn’t be happier,’’ Outteridge said on Sunday.

The pair came from 27th in the fleet to seventh with a day of racing remaining. They then clamoured up the ladder to finish second overall to the New Zealand pairing of Peter Burling and Blair Tuke.

When Outteridge and Jensen sailed past a dead dog as they trained for a Rio Olympic test event they though things were bad. But nothing had prepared them for racing a world title in dark brown water and at a venue where a third of the fleet had fallen ill.

Fortunately Jensen was able to drag himself from his sick bed for a few hours each day to keep he and Outteridge in contention for a world championship medal less than a year out from the Rio Olympics.

“Gooby (Jensen) is still not really well,” Outteridge said last week.

“He was taken straight home from the boat after the race again today and I sailed in by myself.

“ During racing he’s fine, but it’s really difficult to maintain any enthusiasm and energy levels when you can’t eat, because anything he eats comes straight out of him again.

media_camera Sailors competing in the muddy brown water in Argentina.

“He really hasn’t eaten for two days now, so hopefully he can get some more rest and be ready for Gold fleet tomorrow.”

While Australian sailors now go to Rio with numerous precautions to help them stay well in the polluted waters, no one was expecting similar health dramas in Argentina.

Regatta officials confirmed numerous sailors at the 49er and 49er FX women’s skiff championships have fallen ill with stomach and gastrointestinal issues.

media_camera Sickness has hit the fleet at the world 49er and FX 49er world championships being sailed on a brown river in Argentina.

“Recent thunderstorms and some capsizing into the less than desirable looking brown water have been targeted as the culprits for this mystery sickness that seems to be catching up with sailors as the days progress,’’ regatta officials said in a release.

“We don’t really know why everyone is getting sick, but at least a third of the fleet has come down with stomach pains, diarrhoea and vomiting,’’ Outteridge said.

“Obviously the water here isn’t very clean and with the thunderstorms and lots of rain there’s a lot of crap that’s being pushed on to the racecourse and we’re subject to this.

media_camera Iain Jensen and skipper Nathan Outteridge are medal favourites for Rio.

“It’s like sailing in Rio and you have to take the right precautions. In Rio everyone knows it’s dirty and takes precautions accordingly and looks after themselves. Here everyone gets told it’s just muddy water, but there’s a lot of filth in there as well.”

Outteridge and Jensen, who are key players in the Artemis America’s Cup campaign, are multiple world champions and hopeful of defending their gold they won together in London in 2012 in Rio.