Will Wall Block Carp? Invasive Asian Fish Surge Toward Great Lakes

The subject of building walls may be a hot topic right now, but environmentalists and business interests alike are banking on a different kind of wall blocking the advance of invasive Asian carp. The wall will effectively cut off the Mississippi watershed from the Great Lakes watershed and is just one of many efforts to block Asian carp from entering the Great Lakes.

Several species of Asian carp have been present in the Mississippi River basin since the 1970s, where the invasive fish have caused problems by out-competing native species. In the intervening decades, these invasive carp have spread throughout the entire watershed, but they have yet to break into the Great Lakes in large enough numbers to establish a breeding population.

The latest effort to block Asian carp from entering the Great Lakes is a 2-mile-long wall that is actually a massive dirt berm that stands 10 feet tall and 80 feet thick according to the Fort Wayne Journal Gazette. The dirt wall divides the Eagle Marsh wetland in Indiana, which drains into both the Great Lakes watershed and the Mississippi watershed.

The $3.5 million project used federal funds to move nearly 180,000 cubic yards of dirt from elsewhere in Eagle Marsh to construct the berm, according to the Fort Wayne News-Sentinel.

"The berm [was] created out of dirt that we made onsite," Betsy Yankowiak, director of preserves and programs for the Little River Wetlands Project said of the wall. "We were able to deepen, and create shallow water wetlands, and harvest that dirt to build a berm that is 9,000 feet long, about 80 feet wide, and about 10 feet tall. And it stretches throughout the entire Eagle Marsh."

Without the wall, experts fear that Asian carp could enter Eagle Marsh from the Wabash River, which drains into the Mississippi River basin. During flood conditions, the invasive fish could then cross the wetland, enter the St. Marys or Maumee Rivers, and eventually reach Lake Erie.

If the carp were somehow able to reach Lake Erie, they would likely out-compete local fish, causing untold damages to the billion dollar Great Lakes fishing industry.

Prior to the construction of the massive dirt wall, a temporary fence was all that stopped Asian carp from slipping into the Great Lakes watershed during flood conditions.

At the time the wall was completed, the presence of Asian carp had been confirmed in lakers and streams just 20 miles away from Eagle Marsh.

While Asian carp are considered invasive in general, there are actually a number of different species that have been introduced to the Mississippi watershed. According to the National Wildlife Federation, Asian carp is a catch-all term that refers to bighead, silver, grass and black carp, all of which have been found in the wild in the Mississippi River basin.

The most well-known is probably the silver carp, which exhibits the peculiar behavior of launching itself into the air at high speeds. Silver carp have been the subject of a number of viral videos, but all species of Asian carp are voracious filter feeders that are capable of eating up to 20 percent of their body weight each day, leaving little food for native fish.

In some parts of the Illinois and Mississippi Rivers, Asian carp have been so successful that they represent more than 97 percent of the biomass in those bodies of water. If the same thing happened to the Great Lakes, it could be devastating to both the environment and to the fishing industry.

Although the massive dirt wall spanning Eagle Marsh may have halted the advance of Asian carp toward the Great Lakes via that particular vector, the National Wildlife Federation reports that these highly invasive fish could still find a way out of the Mississippi River basin. Another area of concern is the Chicago Area Waterways System, where live Asian carp have been found mere miles away from Lake Michigan.

[Photo by AP Photo/John Flesher]