It took detective work to locate the source of a cancer-causing chemical at Donna Lake. The Environmental Protection Agency has been working for years in the canal system on the issue.

Gravel lines the new banks just dredged by the federal government. The EPA believes a canal leading to the lake had most of the cancer-causing polychlorinated biphenyl (PCB).

PCB was popular in the 1960s for industrial purposes and has since been banned for use, but is still at the bottom of the waters. The chemical is found in the tissue of fish that are in the water. It’s not floating at the surface, because it’s oil-based.

After years of investigation, dredging to remove a large concentration of the contaminant is complete.

Watch the video above for the full report.