MINNEAPOLIS — There’s a back door for Asian carp to sneak into Minnesota, and fisheries officials are worried that the invaders might have found it already.

Commercial fishermen recently caught dozens of Asian carp in northwestern Iowa’s Great Lakes, one of that state’s most popular vacation spots. Those waters connect with lakes and streams in southwestern Minnesota, so the haul came as an unwelcome surprise to Minnesota officials who’ve been more focused on the higher-profile fight against Asian carp infiltrating up the Mississippi River.

“We view it as a big threat. …These fish don’t recognize political boundaries,” said Ryan Doorenbos, area fisheries supervisor for the Minnesota Department of Natural Resources in Windom.

No bighead or silver Asian carp have been caught in southwestern Minnesota, but a few have been netted on the east side of the state in the Mississippi and St. Croix Rivers. Officials have been trying for a few years to develop a strategy to stop them from advancing up the Mississippi past Minneapolis, but they’ve just started studying their options for the southwest.

Iowa DNR officials knew they had a problem when they netted two bighead carp in East Okoboji Lake last August. That was confirmed in late March when commercial fishermen caught 82 bighead carp and 55 silver carp in the same general area. A few days later in Spirit Lake, just below the Minnesota border, they caught one more silver carp, the kind known for leaping high into the air when startled by passing boats.

Officials believe the invasive carp made a dash into the Iowa Great Lakes during record flooding caused by heavy rain last summer. They’ve been present in the Missouri River system for some time. When the swift swimmers finally got an opportunity to sneak past a dam blocking their advance up the Little Sioux River, they were able to reach and swim up a creek that serves as the outlet for the chain of lakes.

The Iowa DNR plans to install an electric barrier to try to prevent reinforcements from reaching the lakes. Biologists don’t know if the fish will be able to establish a permanent breeding presence in them. Research indicates Asian carp need the currents of major rivers to spawn successfully, but neither state wants to take a chance on the fish adapting.

Minnesota started taking defensive measures a few weeks ago. Effective April 30, Minnesota designated several lakes, rivers, creeks and drainage ditches in Jackson and Nobles counties as infested waters because of the risk that a vanguard of Asian carp might already be lurking there.

Luke Skinner, the Minnesota DNR’s invasive species program supervisor, said the main benefit of that pre-emptive strike is that it prohibits the harvest of minnows from those waters that could be used as bait elsewhere.

It’s hard for most people to tell baby Asian carp from native minnow species, so the DNR fears that an angler who illegally dumps leftover minnows harvested from infested waters into another lake could give them a new foothold, possibly even in a major recreational lake well beyond the affected corner of southwestern Minnesota that’s in the Missouri River watershed.

Doorenbos said he’s studying three potential infiltration routes from Iowa. One would be directly from the Iowa Great Lakes via Little Spirit Lake, which straddles the border and connects with several lakes on the Minnesota side. A second would be the Little Sioux River, which starts in Minnesota and flows down the west side of the Iowa Great Lakes before it eventually reaches the Missouri River. The third would be in the far southwest corner of the state near Luverne in the Rock River watershed. The Rock River flows south into Iowa and hooks up with the Big Sioux River, which then connects with the Missouri. While there’s a dam on the Rock River in Iowa, he said it might be too low.

Some fortifications are already in place on the Minnesota side— grates that were installed earlier to block the spread of common carp. They’ll stop big fish, Doorenbos said, but younger, smaller fish can slip through. And the DNR closed a diversion gate between the Rock and Little Sioux watersheds earlier this spring.

The threatened Minnesota waters might not be big destinations like some of the state’s most popular lakes farther north, but they’re important to anglers in southwestern Minnesota as well as Iowans, Doorenbos said. Several, including Loon, Pearl, Rush, Clear, Round and Indian lakes, are managed for walleyes and northern pike and also hold crappie and perch populations, he said.

The Iowa Great Lakes, however, are one of that state’s top tourist destinations, worth more than $200 million annually to the local economy, which is why officials there are so concerned.

“For Iowa this is one of our premier natural resource areas. There’s a lot of interest in getting this area protected,” said Mike Hawkins, a fisheries management biologist with the Iowa DNR.

Fortunately, Hawkins said, the Asian carp caught in the Iowa Great Lakes have all been small, around 14 to 15 inches, suggesting they’re probably only a year old. If they don’t reproduce, their ranks won’t swell unless future flooding allows more of them to enter. And he said there are some indications that silver carp don’t jump as much when they’re in lakes, which would reduce the danger of injuring boaters.

But while the carp hauls have been small — and decreasing — ever since the big catch from East Okoboji in March, that doesn’t mean there aren’t a lot more hiding out there. They grow rapidly to huge sizes and consume enormous amounts of plankton, he said, so they still have the potential for disrupting the food chain and harming game fish populations.

Hawkins said the Iowa DNR is moving as quickly it can to install an electrical barrier at the Little Gar Lake outlet to the Iowa Great Lakes in hopes of preventing any more Asian carp from reaching them. The agency hopes construction can begin this fall.

“Getting that door closed is an important priority for us,” Hawkins said.