We've gone from world-class fishery to a world-class mystery.

Pennsylvania's smallmouth bass have had a rough decade.

First, the fish that helped make summertime fishing in the Susquehanna a draw to anglers across the nation started to disappear at an alarming pace. And now, a new mystery pops up. Anglers are catching "blotchy bass."

Fish are being pulled from waterways across the state with irregular black spots. Sometimes the spots are small. Other times they can be found on as much as half the fish's body. What they are and exactly what causes them is the latest mystery in the smallmouth bass saga.

But unlike whatever is killing the bass in a critical section of the Susquehanna River, "blotchy bass" are otherwise healthy.

"It's not precisely known what causes the condition, but the bass that our biologists examined in previous years were generally healthy and in good condition," said Andy Shiels, deputy director of operations for the Pennsylvania Fish and Boat Commission. "While the appearance of these spots may be alarming, there is no harm to human health from consuming these fish."

In fact, this is not a new phenomenon. In 1986, scientists studied largemouth bass populations across the country and found bass with similar spots in 11 states.

Over 25 years later, we still don't know what causes the spots. It has yet to be linked with a specific type of pollution and bass with the irregular black spots have been found in waterways ranging from the Susquehanna River to Lake Erie. It also doesn't appear to be a phenomenon that affects bass born around a specific time.

In other words, what causes "blotchy bass" is a mystery.

It is a similar situation with the Susquehanna River. Over the last decade, fish with irregular lesions and sores have been caught at an increasing frequency.

But whatever is making these fish sick is also killing them. The river's famed smallmouth population -- the same one that helped launch an industry a generation ago -- is a fraction of what it once was.

The problem is so bad, in fact, a new set of rules were put in place last year. For much of the Susquehanna and the Juniata rivers, bass fishing is strictly catch and release.

Even more aggressive, the fishery in these areas is entirely closed from May 1 through June 15. Find another species to target when bass are in their critical spawning period.

I wish the news was different. It would be great to share a tale of a rebounding fishery that we could boast to the world about. But sadly, that's far from what is happening.

We've got a serious case of sick fish. It's a mystery I hope we solve soon.

Andy Snyder writes about the outdoors for The York Dispatch. He can be reached at sports@york dispatch.com.