The Queensland Government says it may be weeks before it knows the reason behind the deaths of several thousand fish in the Brisbane River at Lowood.
The Department of Environment and Heritage Protection (DEHP) will test water and fish samples, after catfish were found floating along the creek bank at Lowood last week.
Crews from Somerset Regional Council and Seqwater are expected to continue the clean-up today.
"The majority of the dead fish are located around Lowood with small numbers being found further upstream as far as Lockyer Creek," he said.
"There's been no reported fish deaths in other parts of the Brisbane River.
"Somerset Regional Council and Seqwater have both provided great support in volunteering people and resources to assist with the clean-up."
Mr Connor says officers are trying to determine the cause.
"Our officers have taken water samples and samples of the fish for laboratory analysis and we'd expect to have results back from that within around two weeks," he said.
"It is a large kill - it started relatively small last week when we were notified but the numbers have continued to increase over the weekend to the point of several thousand."