Sulfuric acid that spilled from a derailed train in northwest Queensland has reached a nearby creek, police say.
Water testing around the crash site has come back positive for the toxic chemical at Horse Creek, a small slow-flowing waterway.
"There's been some sulfuric acid leakage. The advice back is there has been some impact on the waterways," Inspector Trevor Kidd of Mount Isa police told AAP on Thursday morning.
Emergency services are now finally able to reach the site after heavy rain and flooding hampered access following the disaster on Sunday.
"It's been leaking around the wreckage and into Horse Creek from the site," Insp Kidd said.
"Initially there was no impact on the creek but more recently there's been some impact."
He added there were no high-flowing waterways near the site, but the threat of more rain could spread the acid over the flat flood plains in the area.
The train was carrying 819,000 litres of the highly corrosive acid of which 31,500 litres is believed to have leaked from one carriage.
Construction workers have spent the past few days laying walkways over the flooded site so chemical specialists can reach the wreckage.
"As of a result of the access, we can make some much detailed assessments of what the leakage may be and what's occurred," Insp Kidd said.
Helicopters will distribute limestone over contaminated areas to neutralise the acid while sandbags will line the wreckage to stop the spread of the chemical.
