The mystery has been solved: that mysterious purple water spotted in Denver last month was caused by a spill at a construction site.

The water was reported to 9NEWS in late March at the pedestrian bridge at City of Cuernavaca Park, close to downtown Denver. No smell, just purple color.

When we went to investigate 24 hours later, the river was back to looking normal.

RELATED: Why was the water in a Denver river purple?

We followed up via e-mail with Nancy Kuhn, a spokeswoman for Denver's Department of Public Works, who spoke to us last time about the purple river.

In March, we were told there were hundreds of ways the mystery coloring could have discolored the river.

But, now we know specifically what caused it.

Construction sites near the purple water sightings were examined, Kuhn said.

A spill at one was found, with a compound called potassium permangranate (forget three times fast, try saying that once) in a dewatering project.

A notice of violation was issued for the spill, and monthly inspections of the site are being conducted, Kuhn said.