Haiti - Since Isaac stormed through this island country, streams of dirty water run through many of the tent camps earthquake refugees call home.

Floods represent the main threat, aid workers say. They not only destroy the fragile tents, but also bring with them a range of diseases, from stomach illnesses, to skin infections, to parasites, doctors here fear.

At the Marassa tent city in Port au Prince, residents feared what the storm would do to La Riviere Grise, or the gray river, named for its dirty color. After more than more than 24 hours of rain Saturday, La Rivere Grise became a fierce current that flooded part of the camp. Refugees who had been able to accumulate key survival belongings since the earth shook on Jan. 12, 2010 -- a tarp, a cooking pan, some clothes -- lost all again, in a few minutes.

The situation is similar in post-earthquake camps outside Port au Prince. Some tents survived the storms, others were blown away, shredded or buried under mud.

The Red Cross is among the many non-profit groups distributing tarpaulins, hygiene kits, and aquatabs to purify the water. "The Red Cross is particularly concerned with those who remain in camps, and particularly pregnant women, children, people who have disabilities and older people, who are hugely at risk," said France Hurtubise, communications coordinator for the International Federation of Red Cross and Red Crescent Societies.

But at Port au Prince's main open market, it was clear the city's resilient residents are trying to go on as normal, or normal for this city that has seen so many disasters.

Vendors peddled their wares on Sunday, from fruits and vegetables, to smoked fish, to clothes and small household appliances. Maquelie Octavius has had a vegetable stand there for years. She said Isaac was not going to keep her from working today. "I have no fear," she said, "I have to eat."