“In Western Pennsylvania, folks go downriver for their shopping and entertainment.”

So observed one municipal politician and industrialist from neighboring Mercer County several years ago. Mercer County is, of course, upstream from here, as most of us already were aware.

Still, it’s worth noting this week because our expendable dollars aren’t the only things that flow downstream. The streams themselves do, too — flow downstream, that is — and that’s cause for concern when the state advises us that fish inhabiting these waters are too saturated with industrial waste to be safe for consumption.

On Monday, the Pennsylvania departments of Agriculture, Environmental Protection, and Health and the Pennsylvania Fish and Boat Commission issued a do-no-eat advisory for all fish species caught in the Shenango River in Mercer and Lawrence Counties due to extremely high levels of polychlorinated biphenyl (PCB). The advisory extends to all fish between the Shenango Lake Dam and the mouth of the Shenango River in New Castle.

A do-not-eat advisory already was in effect for the Shenango for muskellunge, carp and channel catfish. The new advisory adds to that list all other gamefish — smallmouth and largemouth bass, bluegill and walleye.

On the face of it, Butler County dodged a bullet. Wolf Creek is the primary stream from Mercer County that drains into Butler County via Slippery Rock Creek in Worth Township; the Slippery Rock flows into the Connoquenessing Creek near Ellwood City. The Conno merges with the Shenango and Mahoning Rivers near New Castle to form the Beaver River, the first downstream tributary of the Ohio River.

There’s a purpose behind this geography lesson. The streams of a watershed are all connected like the blood vessels in a living body — if you inject a drug into one vein, then the entire body gets the effect.

PCBs are not drugs, but they are poison. The man-made compounds were once used in a broad variety of applications especially as lubricating, coolant and hydraulic fluids. But PCBS fell out of favor when they were identified as a cause of cancer and a wide range of other adverse health effects. There are a number of serious non-cancer health effects in animals including effects on the immune system, reproductive system, nervous system, endocrine system and other organs.

Tissue samples taken from fish found some levels of PCB to be more than 22 mg/kg in smallmouth bass, which is more than 10 times the no-consumption advisory level of 1.9 mg/kg.

DEP has recruited federal EPA assistance to investigate possible sources of the contamination, which DEP Secretary Patrick McDonnell described as “very high.” But Congress banned U.S. manufacture of PCBs in 1979, which means the likely source of contamination an industrial dumpsite that’s slowly leaching.

In theory, the source of contamination should be easy to find. Just go upstream until you can’t find contaminants anymore. The strategy can’t fail if you’re testing water. But the PCBs aren’t showing up in the water; they’re showing up in the fish — which, unlike the people and the water of Western Pennsylvania, are as apt to migrate upstream as they are down.

This could be an arduous hunt. It could become a witch hunt. Will EPA/DEP locate the source of PCB contamination? Can they identify a responsible industry? Does the polluter still exist as a corporation? Does it have assets and/or responsible corporate officers?

There may be broader questions: Wil the search reveal a potential Superfund site? Is there funding to pursue another Superfund project? What’s the future of the Superfund program? Will future federal budgets provide sufficient funding?

Meanwhile, give recognition to recent continued focus on clean water projects like the Allegheny Aquatic Alliance. Its volunteers on Saturday pulled hundreds of tires and other trash from an 18-mile stretch of the Connoquenessing Creek between Harmony Junction in Jackson Township and Ellwood City. This year marked the sixth annual creek cleanup organized by the alliance. Well done.