Rehabilitation of the marsh and lake habitats at the Hennepin and Hopper Lakes Project has begun this fall through the joint efforts of the Illinois Department of Natural Resources (IDNR) and the Wetlands Initiative (TWI).
The efforts will focus on removing the destructive common carp, which has been wreaking havoc on the aquatic ecosystem since 2006. The invasive, bottom-feeding carp stirs up the lake bottom, rooting out plants, reducing water clarity, and ultimately destroying the marsh habitat.
“It’s time to bite the bullet and remove the carp,” said Al Pyott, TWI board member and co-founder. “It’s painful because we’ll lose the lakes for a year, but it has to be done to restore the entire habitat for all the species that depend on Hennepin and Hopper.”
“This aquatic rehabilitation project is designed to re-establish Hennepin and Hopper Lakes as an important backwater lake area,” said Wayne Herndon, IDNR district fisheries biologist. “We have very few of these vital habitats on the river that depend on vegetation to maintain water quality, so it’s critical that we regain this marsh habitat.”
The 2,600-acre Hennepin and Hopper Lakes Project, located along the Illinois River south of Hennepin, is owned by TWI and several nonprofit organizations and is managed by TWI.
Since 2001, TWI has been restoring the historic lakes to create a high-quality backwater lake habitat in order to improve water quality, provide wildlife habitat, and to offer a place for the public to enjoy Illinois’ historic native landscapes.
Prior to 2001, the lakes had been drained for 90 years to support corn and soybean farming. The lakes were opened to public fishing in 2004.
“This area is very important for waterfowl because it is at the turning point of the central flyway, where ducks traveling from the northwest turn south at the Big Bend of the Illinois River,” Herndon said. “The more attractive the habitat is for waterfowl, the better the flyway is for all.”
The project was dedicated as the Sue & Wes Dixon Waterfowl Refuge in 2005 in recognition of the critical waterfowl habitat that the site provides. Since 2006, common carp have been disrupting the lake ecosystem and the waterfowl population has steadily declined. Last fall the total number of migrating waterfowl dropped by 90 percent from its peak in 2004, according to IDNR surveys.
To begin the rehabilitation, TWI has turned on the drainage pump at the south end of the lakes, sending lake water into the Illinois River.
Draining the lakes alerts the reptiles and amphibians to move to new habitat. Dr. Gary Sullivan, TWI’s senior restoration ecologist, said he expects most of the turtles, snakes, frogs, and salamanders to survive and return when the lakes refill next year.
By electrofishing near the pumps, Herndon and his crew will be able to rescue some of the game fish still in the lakes. Fisheries staff will hand-select the desirable fish and move them into the river.
As the final step to removing carp, IDNR fisheries staff will apply rotenone in early spring. Rotenone is a natural extract from the roots and stems of a tropical plant and has been used since the 1930s for managing invasive fish populations.
Because rotenone decomposes rapidly in sunlight, Herndon expects to restock the lakes within 2-3 weeks after the rotenone application is complete.
As the lakes naturally refill with groundwater and precipitation, they will be a fertile nursery to young game and native fish stocked by IDNR, including largemouth bass, black crappie, bluegill, northern pike, walleye, and sauger. Herndon said he also will stock native species such as starhead topminnow and redspotted sunfish.
Herndon expects the fish to grow rapidly in the recharged food web of the restored lakes.
“By removing the carp, we’ll enable the plants to return,” TWI’s Sullivan said. “Once the plants return, we’ll have clear water again, and the birds, turtles, snakes, otters, and beaver will return.”
The sport fishery will also return in full force, Herndon said. “We could expect to see 13- to 14-inch largemouth bass by spring 2011,” he said.
IDNR and TWI will monitor the growth of the fish population in the coming years before deciding when to re-open the lakes to public fishing.
“We expect this rehabilitation effort to re-set the system for the next 20 to 30 years,” Herndon said. “This is an intrusive operation to the entire habitat and we don’t want to do this often, but we need to preserve these historic backwater lakes when we can, particularly when they are already separated from the river by a levee.”
Herndon said the restocked fish will thrive in the healthy, diverse ecosystem that will develop in the isolated lakes, and the new fish will keep any future young carp in check.
In 1986, IDNR launched a similar aquatic rehabilitation effort at Spring Lake State Fish and Wildlife Area, 25 miles south of Peoria. Since then, the carp population has been kept in balance naturally.
IDNR and TWI will host an information session for the public on Monday, Oct. 26 at 11am at the Hennepin and Hopper Observation Tower.
For more information, visit wetlands-initiative.org or call Wayne Herndon (IDNR) at 309-968-7531.
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