Part of Townleys Rd, in Kaikorai Valley, was closed for about 18 hours, due to a major spill of offal from a truck.
The Otago Regional Council had spoken to the trucking company involved, but said it was too early to know if a prosecution would be considered, in response to a pollution complaint.
A witness, who asked not to be named, believed the animal product seeped into the Kaikorai Stream.
It was also not uncommon for there to be a spill in that area; spills occurred about once a week, although usually on a smaller scale, he said.
ORC regulatory general manager Richard Saunders said the investigation would determine the substance, which ORC staff at the scene were told was blood, and whether there was an environmental effect.
"During our initial response to the incident staff did not identify contaminants entering the stream."
The trucking company had organised for grit to be placed on the road and gutter, and hay bales for bunding to manage the contaminants, he said.
ORC staff did not see any sign of contaminants in the stream during a follow-up inspection on Monday.
Mr Saunders said apart from one complaint in 2017, the council had not been made aware of offal spills happening regularly.
The witness described the spill as ‘‘thousands of litres of blood and guts’’ — tipping out of a truck navigating a steep uphill section near the Kaikorai Valley Rd intersection and above a bridge crossing Kaikorai Stream.
A Fire and Emergency New Zealand spokesman said firefighters, along with representatives of the Otago Regional Council and Dunedin City Council, were called to the scene, but it was too extensive for Fenz to deal with, and no washing up action was taken.
