At a printed circuit shop in the Bay Area near Los Angeles, there was trouble with the copper plating line. Plating is one of the key processes for making printed circuits.
The plating tanks would not work.
The blue copper-plating bath would turn an off color and get cloudy. This color change would even happen when no parts were being run, and no new chemicals were being added to make a fresh plating bath.
The plant had an excellent water purifier and state-of-the-art micro-filters that weren't picking up on any contaminants during routine analysis.
Nothing was detected in a chemical analysis in which the level of metal ions was checked.
Was an impurity getting into the tank and how?
Here's the rest of the story.
The plating line technician mentioned the problem to a friend who had the job of testing water at the county water supply facility. He pointed out that fine pollen from big redwood trees in the area were clogging filters in the water works, so they were experimenting with courser filters.
The pollen level would drop off by March, so it was a matter of getting through the winter months. Armed with this information, the technician looked for pollen in the cloudy plating bath. Further detective work showed that the pollen was getting through the circuit factory filters and precipitating certain chemicals.
Experts in the field of water purification estimate that 90% of factory water problems are due to natural contamination of the incoming water. Nature strikes back, and often.