Forecast warmer temperatures may be welcomed by many Victorians after a cold, wet October but it could mean more fish will die in the flood-affected state as a result.
The Environmental Protection Authority's (EPA) chief environmental scientist Mark Taylor said water testing in several locations, particularly in northern Victoria, was showing dissolved oxygen levels below the minimum 20 per cent native fish required.
"The toll on Victoria's inland aquatic wildlife from the floods is tragically going to grow as we see a combination of flood affected waters and warmer weather both of which will reduce dissolved oxygen levels," Professor Taylor said.
"Our advice is to continue to avoid contact with floodwaters where possible because of the risk of contamination, not to eat any dead fish found in the waters and in the first instance, report dead fish sightings to EPA."
Regional floodwater testing by the authority found better than expected results in most locations when it came to contamination, with very high levels of E. coli only detected at Shepparton in northern Victoria.
Water from the Goulburn River at Shepparton tested E. coli levels at more than three and a half times the guideline level.
Lake Nagambie, Campaspe River at Kyneton, Broken River at Benalla, Loddon River at Kerang, Campaspe River at Rochester, Coliban Pool at Lake Eppalock all tested well under the E. coli guideline number.
"These results are only indicative but show a similar picture to what we found in other floodwater tests at the Maribyrnong River with a better than expected outcome," Mr Taylor said.
The Victorian State Emergency Service will keep providing samples to the EPA in the coming weeks to keep communities informed about potential water contamination issues.
Dead fish sightings can be reported at 1300 EPA VIC (1300 372 842).