Scientists are already testing for Asian carp DNA in the Great Lakes. (Department of Natural Resources)

The Obama administration will spend about $50 million in 2012 to shield the Great Lakes from greedy Asian carp, including first-time water sampling to determine whether the destructive fish have established a foothold in Lakes Michigan and Erie, officials said Thursday.

An updated federal strategy for preventing an invasion also includes stepped-up trapping and netting in rivers that could provide access to the lakes, as well as initial field tests of chemicals that could lure carp to where they could be captured, officials told The Associated Press. An acoustic water gun that could scare the carp away from crucial locations will be tested near a Chicago-area shipping lock that some want closed because it could serve as a doorway to Lake Michigan.

"This strategy builds on the unprecedented and effective plan we are implementing to keep Asian carp out of the Great Lakes while we determine the best long-term solution," said John Goss, the Asian carp program director for the White House Council on Environmental Quality.

The underwater gun, which emits piercing blasts of pressure and sound, will be tested near the O'Brien Lock in Chicago, which Michigan and other states have asked federal courts to close because the carp could swim through it to reach Lake Michigan.

"We're working on a possible strategy to fire these guns prior to opening locks to deter fish from coming into the area," Goss said.

Goss said initiatives in 2012 would "strengthen our defences against Asian carp and move even more innovative carp control projects from research into implementation."

Millions budgeted to mount defence

The federal government has already budgeted more than $100 million over the past two years in the fight against bighead and silver carp. They were imported from Asia decades ago and have migrated up the Mississippi River and its tributaries since escaping from fish farms and sewage lagoons in the Deep South. They have infested the Illinois River, which leads to Lake Michigan.

The carp eat massive amounts of plankton -- tiny plants and animals at the base of the aquatic food web. Scientists differ about how widely they would spread in the Great Lakes, but under worst-case scenarios they could severely damage the $7 billion fishing industry.

The U.S. Army Corps of Engineers is studying how to stop species migrations between the Great Lakes and Mississippi River watersheds, particularly through rivers and canals in the Chicago area. Five states -- Michigan, Minnesota, Wisconsin, Ohio and Pennsylvania -- are suing in federal court to speed up the study, due for completion in 2015.

Several independent studies, including a report last month by the Great Lakes Commission and the Great Lakes and St. Lawrence Cities Initiative, have called for placing barriers in the Chicago waterways to sever a manmade link between the two drainage basins.

Plans have some opposition

Environmentalists favour doing so, but Chicago business interests oppose it, saying it would damage the region's economy and cause flooding.

The Obama administration has not endorsed separating the systems. Goss told the AP the idea "deserves complete analysis" but said he was concerned about estimates the job would take nearly two decades.

"That's why the technologies we're working on for Asian carp control and detection are very important," he said.

The centerpiece of the federal effort to protect the lakes is an electronic barrier network in a shipping canal southwest of Chicago. The administration's plan calls for expanded underwater surveillance this year to make sure it's keeping the carp at bay.

Dozens of water samples taken beyond the barrier in recent years have contained Asian carp DNA, although just one actual carp has been found there. Expanded sampling this year will look for signs of the invaders at about 10 locations in southern Lake Michigan and western Lake Erie. They are considered among the likeliest places in the Great Lakes where the carp could become established, partly because of nearby tributary rivers suitable for spawning.

Commercial fishermen have been hired to reduce carp numbers in the Illinois River below the barrier. They'll be provided with new types of nets and other equipment this year to boost the harvest, Goss said.

"As the population is reduced in that area, they're becoming more difficult to catch with traditional netting," he said.

Some funding for the Asian carp program has come from the Great Lakes Restoration Initiative, a federal plan to fix the region's biggest environmental problems. President Barack Obama has requested $300 million for the program in 2013 on top of $1 billion appropriated since 2008.