State environmental officials lifted an advisory against swimming in Southeast Georgia's Ogeechee River late on Friday.
A warning against fishing in the river, however, remains in effect.
Environmental Protection Division officials say, a bacteria started a massive fill kill on the river late last week.
The fish kill was unusually large and made its way from the river's headwaters all the way down to the coast.
The bacteria, columnaris, isn't known to affect humans, but officials still want people to avoid fishing until they can do some more tests on the fish.
The Ogeechee Riverkeeper's Executive Director Emily Markesteyn says, the big mystery isn't what bacteria killed the fish but what else might have weakened the fish to make them succomb to the bacteria.
"We want to know the answer," Markesteyn says. "It is a very scary thing when you don't know what's going on."
The Riverkeeper is conducting its own tests, separately from EPD, to determine what might have stressed the fish.
"That stressor could be anything and it could affect humans," Markesteyn says. "It's just really important that we find that out."
The stinking rot came at a bad time for businesses dependent on river tourism.
Legions of boaters typically flock to the slow-moving Ogeechee River for Memorial Day weekend.