DECATUR — Five years after the approval of a $120,000 fence at the Lake Decatur dam to prevent jumping Asian carp from invading during a major flood, the coast is clear — for now.
The non-native fish have been spotted in the Sangamon River downstream for years, and the fence over the dam's locks makes it even harder for the agile swimmers to leap into the lake. But the types of Asian carp in Illinois are so good at reproducing, there's only so much state and local officials can do.
"I hope to heck they never get in there," said Joann Lowe, owner of Mike's Tackle World on East Geddes Avenue in Decatur. "You can't go fish, you can't go in the boat, you can't go water ski, you can't do anything — they take over."
They're not always there depending on the season, but city officials said the pond directly on the other side of the lake from the dam can host thousands of carp after a major rain event.
"In the spring, when we're discharging a lot of water (from the lake), and they're trying to spawn, they're thick in the downstream side of the dam," said Matt Newell, Decatur public works director.
The dam's 4-foot fence, made in part with metal floor grating, is designed to be an additional barrier to the silver carp, the most fidgety of the Asian carp species, able to jump up to 10 feet in the air.
"When we have really long spring rain events, we are releasing billions of gallons of water a day (from the dam)," said Keith Alexander, the city's water production manager. "That causes the river (downstream) to rise — it'll come within 10 feet of the top of the lake surface. That's where some of these very athletic Asian carp can make that jump."
The dam crosses the Sangamon River northwest of the U.S. 51 bridge. The lake was created in the 1920s by damming the Sangamon and is the primary source of drinking water for the community and for use by industries. Currently, another $91 million is being spent on a extensive project to dredge the lake.
The fish barrier was part of a $4 million upgrade to the dam in 2013 and 2014. The engineering firm Hanson Professional Services, which designed the fence, calculated the additional barrier would prevent the strongest carp from jumping into the lake in anything up to a 100-year flood event.
But other than the fence, "There's nothing we can really do to watch and guard against it," Newell said. "So once it happens, it happens — it's not like we could lower the lake, or lower the backside of the dam, we would be facing what we face."
Not only can the carp species eat close to their body weight of plankton a day, siphoning a crucial food source for hundreds of native fish species across the region, they're a nightmare for human recreation on lakes and rivers.
"Their tendency to jump out of the water means there's a safety hazard as well, there's always that potential where there could be human harm," said Scott Collins, a postdoctoral research scientist at the Illinois Natural History Survey. "We haven't seen a lot of those cases, but we've been hit by (carp) when doing work on the Illinois River."
The Asian carp in the United States today comprise mostly of four species of fish originally from China: silver carp, bighead carp, grass carp and black carp. They have been farmed in China and widely eaten there for centuries — they can be found in cuisines all over the world.
But the carp species are extremely resilient, able to eat close to or even above their body weight in plankton — small plant and invertebrate organisms that can be found in any natural water source. They can also reproduce easily and efficiently by spawning more than once a year.
In larger bodies of water they can grow much bigger, but Alexander said the carp he's seen near the dam are about three or seven pounds. "You'll see 2,000 fish and they are identical in size, there's that many of them."
In the 1960s and '70s, U.S. fish farmers and government officials started importing them from China as a new way to eliminate toxic algae growth in enclosed water systems like sewage treatment plants and catfish ponds. According to the Illinois Department of Natural Resources, fish breeders in Arkansas flushed the carp into canals and waterways. Eventually the carp found their way into the Mississippi River, and over a period of decades, the carp populations thrived and grew in rivers and tributaries throughout the South and Midwest.
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From South Dakota to Louisiana, Asian carp continue to thrive and their voracious appetite is threatening the ability of native fish species to survive. "They can out-compete native fishes for the food they eat," Collins said.
Environmental scientists struggle sometimes to convey to the public the harm of invasive species, but not with Asian carp. They pose a threat to commercial and recreational fishers and even boaters looking to enjoy a day on the river or the lake.
Not only do the vibrations of boat motors cause silver carps to leap out of the water by the dozen, they can ruin traditional sport fishing.
"What they're eating is very small invertebrates in the water, so they don't bite at a lure like the native walleye other species would," Collins said. "There's no way to hook and line a carp species."
Lowe said some in the Decatur area used to travel to near Peoria area for fishing on the Illinois River. "Nobody goes now," she said. "(The carp) have taken over big time."
Hobbies like boating and water skiing have become extremely unpleasant if not outright dangerous in waters like the Illinois River, thanks to the huge numbers of carp that fly through the air from the vibrating boat engines. YouTube videos abound of water skiers finding creative ways to impale flying carp in midair as they glide behind a speed boat.
The war against carp
State and federal officials have been working in recent years to contain the Asian carp population in Illinois and beyond, and above all, keep them from entering Lake Michigan, a prospect that would devastate a multimillion-dollar commercial fishing industry there.
Federal and state officials are closely monitoring electric barriers built by the Army Corps of Engineers in the Chicago canal system that are meant to prevent carp from swimming farther upstream into Lake Michigan. Various efforts are underway to stop the species from getting to the Great Lakes.
But for Lake Decatur, the greatest threat is local fishers and boaters either maliciously or accidentally bringing carp into the water from the downstream side of the Sangamon River.
State law prohibits residents from possessing live Asian carp. "If you are going to keep them, especially to eat, the best thing is to pretty much clean them and get them on ice right away," said Mike Mounce, fisheries biologist for the Illinois Department of Natural Resources.
No one has ever reported catching any species of Asian carp in Lake Decatur, according to Mounce. Two reports have come from Lake Shelbyville, but lakes are less likely to keep the fish for long, he said, because the species need a fairly strong current to spawn.
Water in Lake Decatur moves faster than most lakes, he said. "If you get heavy flows it might be a slight possibility."
But there are some best practices for local water sport enthusiasts to make sure they don't bring carp eggs into the lake. Fishers, Alexander said, "want to make sure their live (fishing bait) wells are are clean and dry before they go to any other body of water, because in theory they could ship carp fish eggs in their live well water."
Last, boaters should be careful not to flush out water from their engine systems in Lake Decatur. "Flushing out the outboard engine, inboard engine cooling systems — don't flush it into the lake," Alexander said. "Do it in the driveway or at home because we don't want that water potentially transporting the eggs into Lake Decatur."
"Unfortunately, most of the time fish getting moved is intentional, or somebody turning their bait loose at the end of the day," Mounce said.
Sometimes fishers believe they're doing something good by introducing fish into a new body of water, increasing the chances of better future fishing. "Rarely is that the case," Mounce said.