Patrick Hogan, a city water quality technician, said the substance resembled a naturally occurring iron-oxide bacteria rarely found in a flowing stream.
Hogan walked the creek and found a break in the color near an outfall pipe, he said. He looked at maps of the drainage network, which led him to the treatment plant and the improperly routed pipe.

John McIntyre, operations manager for Crowder Construction, described the situation as an honest mistake. As soon as the problem was identified last week, they immediately fixed it.
​The company hasn’t been fined, but the city is required to report the incident to the state, city officials said.
The improperly connected line discharged liquid from a basin at the treatment plant that uses coagulants and gravity to remove suspended solids from water. The discharge, which flows through a pipe at the top of the basin, is typically clear, but may have a small amount of residual coagulants, Westbrook said.
Hogan did a visual inspection of the creek and didn’t see any dead fish.
The basin’s liquid, which is supposed to be routed to sanitary sewer system, is discharged about once a week and is mingled with groundwater that is pumped out from an ongoing construction area.
It’s not clear why the issue only showed up now if the pipe had been connected since April, city officials said.
To complicate the investigation, the orange substance has also been seen upstream of the plant, Westbrook said.
It’s hard to tell exactly what causes a problem if they don’t see it being dumped in the creek, city officials said.
City officials hadn’t seen the creek turn orange before and it affected from a quarter-mile to a half-mile of the creek, they said.
By Monday, the discoloration was gone, they said.
That could mean that the oxygen levels had changed, that the substance was washed downstream or that it got buried by sediment, said Michelle Woolfolk, with the city’s Stormwater Services.
City officials will do one more follow-up, but will then close the case, Woolfolk said.
Chris Dreps, executive director of the Ellerbe Creek Watershed Association, said illegal discharges into the creek aren’t unusual.
“Something like this really happens once every couple of months,” he said. “Some are less significant. Some are more significant.”
This instance, however, shows the power of people to make a difference in Durham’s ongoing battle to address water quality by reporting concerns.
City officials found 84 pollution sources in the Ellerbee Creek watershed from October 2014 to September 2015, which is 42 percent of the 196 illegal discharges they discovered in 14 city creeks and rivers.