Two lab tests confirm that a smallmouth bass caught in the lower Susquehanna River last year had an extremely rare, malignant tumor, the Pennsylvania Fish and Boat Commission announced.

Officials say this is the only documented case of this type of tumor being found on a bass in the state, but biologists have seen an “alarming rate” of lesions on fish in the Susquehanna, a sign that health of fish in the river is compromised.

“As we continue to study the river, we find young-of-year and now adult bass with sores, lesions and more recently a cancerous tumor, all of which continue to negatively impact population levels and recreational fishing,” PFBC Executive Director John Arway said in a statement. “The weight-of-evidence continues to build a case that we need to take some action on behalf of the fish.”

The PFBC has unsuccessfully petitioned state environmental regulators to declare the Susquehanna River and “impacted waterway” a designation that would force a restoration plan for the river. 

The Pennsylvania Health Department says there is no evidence fish tumors present dangers to humans, they recommend eating fish with lesions. 

The commission says deciding whether to eat fish from the river is a “personal decision.” They have issued advisories urging anglers not to eat several species of fish more than once or twice per month. Small mouth bass are among those species.

For 98 miles of the Susquehanna, including where the fish with the tumor was caught, anglers must release any bass caught.

State and federal regulators are working to investigate what is causing lesions on the bass.