The Bundaberg Regional Council in southern Queensland is continuing to warn residents to take precautions, after a strain of E. coli was detected near Millbank in the Burnett River last week.
Potentially dangerous levels of the bacteria have been found in upper parts of the river.
Dr Lorelle Fabro from CQUniversity says people should also avoid contact with the water.
"What they're worried about is they find E. coli in the water- it's an indicator that there may be faecal human contamination in that water," Dr Fabro said.
"It's very wise not to swim in it, not to drink it and be careful around that water."