They don’t know where it’s from, they don’t know why it’s there, but “mystery goo” is causing headaches at the Elkhart Waste Water Treatment Plant.

The goo is such a problem, it caused operators to divert partially-treated sewage into the St. Joseph River on April 5 and 6. This was to prevent further harm to the facility’s biological water treatment process, according to the Elkhart Truth.

On those two days in April, the plant received three separate hits of bright green water with orange floating goo that had a heavy solvent or paint smell, according to the Elkhart Board of Public Works. The goo caused the microbes that break down waste water to go dormant, which created a serious problem.

The goo is also causing the city to fork over $150,000 for emergency cleanup of one of the digesting units at the plant, along with an additional $22,000 to replace a pump.