The environmental impact of the spilling of up to 3000 litres of diluted weed spray into a Waikato stream is yet to be seen, according to the regional council.
The incident occurred when a small weed-spraying truck veered off Waihi's Waitawheta Rd after the driver was blinded by sunstrike about 7.30am.
The driver suffered minor injuries, Waihi police Acting Sergeant Wayne Harper said.
A statement from the Waikato Regional Council said it appeared the spill had little environmental effect but people were urged to remain cautious over contact with the stream.
The Taiari Stream flows into the Ohinemuri River.
The council's compliance and education manager Rob Dragten said staff had checked water up to 2km downstream from the spill site and had not yet seen ill-effects on aquatic life.
"We're hopeful the spill will have had minimal impact on eels, fish and other stream life but we'd ask the public to be on the lookout and report any signs of problems with aquatic life in the Taiari Stream and Ohinemuri River."
Until the test results are revealed, the Waikato District Health Board advises those in the vicinity to take a precautionary approach and avoid contact with the water.
The Hauraki District Council confirmed there were no risks to public water supplies.