Someone observing San Miguelito Creek near Lompoc called the county reporting faster and murkier water.
When the county and state environmental agencies took a closer look, they found a nearby diatomaceous earth mining plant, owned by Imerys, was leaking run-off used in the mining process.
An investigation shows two pumps carrying the run-off to a storage pond failed, passing water into the creek.
Diatomaceous earth is rock that is very porous; it is used to filter water, swimming pool water and even beer.
A scientist with the California Regional Water Quality Control Board said it made the creek look like "chocolate water."
She tells News Channel 3 that the main impact they are worried about is to the Rainbow Trout.
The fish may not be able to see through the murky water, inhibiting their ability to hunt.
The Board says Imerys is replacing and repairing the pumps and installing alarms to prevent future leaks.
The Board and the California Department of Fish and Wildlife continue an investigation to find out how much diatomaceous earth was leaked and if a cleanup will be needed.