"It's very striking that something would go into a stream that could create that much discoloration," said Gary Gill, deputy director for the State Environmental Health Administration.
The state office that handles chemical and oil spills sent samples to a UH lab. On Friday, tests ruled out pesticides. The next test will look for the presence of titanium dioxide, found in white pigment in latex paint.
"We shouldn't be putting any kind of pollutant, paint, concrete, solvent, pesticides, anything into the storm drain system," Gill said.
He said streams move fast. So do pollutants that get into the water.
"From the mountain to the ocean could be less than an hour," he said. "By the time we arrive, even if it's just an hour later, it may totally be gone."
There's no official estimate on how much stuff was dumped into Keaahala stream, or proof of where it came from.
"In this case neither the police nor anyone who responded from the city or the state was able to find any evidence of where the source of this contaminant might have been," Gill said.
Even an accident violates the Clean Water Act. If found, the culprit could face fines up to $25,000 a day. So far no dead fish have washed ashore.
On Monday, the state hopes to know exactly what made the milky mess.