THE water quality of the Mary River and related creeks is deteriorating, according to research by the Mary River Catchment Co-ordinating Committee.
MRCCC volunteers have spent a considerable part of the past 18 months collecting samples of water from different sections of the Mary River, leading up to this month's marathon "catchment crawl" from Conondale to Tinana Creek.
Catchment officer Steve Burgess said testing over some years had now given the MRCCC a reasonable idea of normal water quality, enabling them to give waterways a rating from A to C.
"We give these sites an A, B, C grading, a bit like healthy waterways report card but our own, based on the physical and chemical quality."
The Mary River as a whole received a B grade, but the results showed the water quality had deteriorated in the past five years.
Mr Burgess said the recent floods were the main cause of the worsening quality, but there had also been an impact from agriculture, especially in the creek systems.
"Over the last three years there have been problems with sediment and soil being carried down the river from the floods," he said.
"That is natural but the fact that we've got river banks which aren't as vegetated as they used to be means there's more erosion than what it might have done if the river banks had been in their natural states."
Mr Burgess told Fraser Coast Chronicle reporter Eliza Wheeler some parts of the water system were in pristine condition, whereas others received fails on their report cards, such as Gutchy Ck.
According to the water quality guidelines, the oxygen percentage of the Mary river catchment should be between 85-100%. Gutchy Ck's oxygen level sits between 25 and 47%.
The data collected will be presented to the State and Federal Governments to improve the current guidelines.
Mr Burgess said many volunteers and businesses had helped with the research.