Commercial fishermen, similar to those in the photo above who netted rough fish just upstream of Prescott, Wis., last spring, recently snagged a bighead carp in the St. Croix River — a catch alarming enough that the Department of Natural Resources' PR machine swung quickly into action to highlight that Asian carp are indeed clawing their way up the Mississippi River, headed for Minnesota.

The bighead is one of four Asian carp species that are much feared by fisheries managers and the public alike. Not least of these critters is the mighty silver carp, known for its wild leaps en masse from the Illinois River and other waters when disturbed by the sound of a boat motor.

Timing of the catch was fortuitous for the DNR, because it and, more broadly, the Dayton administration are lobbying for an approximate $15 million upgrade to the Coon Rapids dam, which they see as a way to thwart, if not block, the rampaging carp from entering waters farther north still, including the Rum River and, ultimately, Mille Lacs and beyond.

If you're wondering how we got here — how it is, for example, that with little or no warning the entire Minnesota River watershed all the way to South Dakota has been ceded to an eventual invasion of Asian carp — you're not alone.

You've got company as well if you wonder why the DNR, the U.S. Fish and Wildlife Service and the National Park Service seem so willing to let the St. Croix River up to Taylors Falls (a natural barrier the fish can't surpass) also become infested with Asian carp — particularly when technology exists that could (thwart, stop, slow — pick one) these bad boys from swimming upstream into the St. Croix at Prescott, Wis.

It's at Prescott that a sonic barrier could be installed that would emit sound and air bubbles to keep carp out of the St. Croix — or at least slow their invasion.

But nothing's being done.

A little history: In 2004, Asian carp were in the Mississippi in Iowa waters far enough south that sonic bubblers could have been installed at one or more lock and dams to keep the invaders south, or at least slow their progress north

Slowing them is important, because ongoing research might stumble on a way to kill the fish, stop them from reproducing or otherwise deal their spread a significant blow.

Credit the Minnesota DNR with this much: It warned our congressional delegation and anyone else who would listen that the opportunity to stop (slow, thwart) the carp in Iowa's Mississippi waters was at hand.

Then Minnesota Rep. Jim Oberstar, among others, heeded the notice, and authority was given by Congress to the Corps of Engineers to install one or more sonic bubblers in Iowa waters. But no appropriation was  made, and without money, the Corps did nothing.

Now the horses quite literally are out of the barn, as silver, grass and bighead carp have all been found in the Mississippi (and/or the St. Croix) well north of Iowa.

But "this is not a crisis,'' according to the Minnesota DNR's Luke Skinner, who runs the agency's invasive species program, because reproducing populations haven't been found here.

Oh, really?

What the DNR in 2004 forgot to say about stopping Asian carp in Iowa waters was this: No other Mississippi River lock and/or dam between Iowa and the Coon Rapids dam is constructed in such a way as to lend itself to the installation of a sonic bubbler (or two or three).

That's why, even if the state (including Wisconsin) and feds decided to get off their hands and try to stop (thwart, slow) Asian Carp south of where the Minnesota River joins the Mississippi, it couldn't — because no lock or dam is suited for the sonic bubblers.

Except at Prescott, Wis., where the St. Croix joins the Mississippi — a sonic bubbler could be installed there.

So why isn't the DNR and particularly the National Park Service — the latter of which enjoys vast regulatory control over the St. Croix — telling anyone who will listen of the importance of installing a sonic bubbler at Prescott?

Money and politics.There's little of the former to go around — a bubbler would cost a reported $4 million (chump change for what's at stake) — and the latter dictates that agencies don't advocate for something that administrations haven't budgeted for.

Minnesota's Gov. Mark Dayton has shown pretty good instincts so far regarding natural resource issues about which he has sufficient information. But it's safe to say he knows nothing of the option of installing a sonic bubbler at Prescott.

The same must also be true for all the rich and powerful people who call the St. Croix their home, or the place they fish, boat or camp. Ditto the many groups and border organizations and towns — Hudson, Wis., and Stillwater to name two — whose very existences are defined by the St. Croix.

They must all be in the dark.

If they weren't, they'd demand that everything possible be done to keep Asian carp out of their home waters.