The Orange County Public Works Department said a mile-long sheen of petroleum in a flood control channel south of Warner Avenue was noticed on Sunday.
Public Works Manager of Environmental Resources Chris Crompton said the sheen did not pass into outer Bolsa Chica Bay or the Bolsa Chica Wetlands.
Crompton described the spill as "fairly small and discrete" with no continuing source. On Wednesday, he said it had largely dissipated or been absorbed by the booms, which have been in place since Sunday.
"What happened was we just had a source within the water and I guess that's good news," Crompton said.
The city's Hazard Materials Unit deployed a petroleum absorbent boom on the upstream side of the tide gate, downstream of the trash and debris boom at the mouth of the flood control channel.
"We still have the booms out there, we had people out there yesterday looking at the situation and the sheen has largely dissipated now," Crompton said. "Right now, there is no real visible sheen left on the water."
California Fish and Game asked the public works department to monitor conditions at that gate for the following days to prevent the sheen from entering the Bay and Wetlands.
"The good news is it didn't continue to get worse; it basically dissipated, which is excellent. We'll make a decision in the next day or two to remove the booms," he said.
— Andrew Shortall