Stopping aquatic invaders
WORTHINGTON -- A little-known slough northwest of Worthington has the potential of saving local lakes from being overrun by the latest aquatic invasive species, the bighead carp, but it also leaves some locals wondering if closing off water from the slough might leave Worthington's wells a bit thirsty.
Herlein-Boote Slough has served as an additional water source for the Okabena-Ocheda Watershed District since a diversion ditch was constructed in the early 1980s to channel water east and ultimately into Whiskey Ditch and Lake Okabena. Prior to the east gate's construction, water from the slough traveled to the Kanaranzi-Little Rock Watershed District, and the intent back in 1983 was to close off that gate and direct all of the water to Worthington.
By the late 1980s, however, it was decided both the west gate and east gate be opened, sending excess water from the slough in both directions, and into two different watershed districts.
Those gates remained open for more than two decades, until the Minnesota Department of Natural Resources stepped in this past winter and closed the east gate. Their reason for doing so, according to Ryan Doorenbos, the DNR's Windom area fisheries manager, is to prevent the bighead carp and another invasive, the silver carp, from moving into the Okabena-Ocheda Watershed District and spreading to the Heron Lake Watershed and Des Moines River basin. If the invasives were to reach those watersheds, they have the potential to infest at least a third of Iowa's waters.
As explained on the U.S. Geological Survey's website, bighead carp were imported into the U.S. in 1972 by a private fish farmer in Arkansas who wanted the carp to eat the phytoplankton in his culture ponds and essentially improve water quality. By the early 1980s, the species were discovered in the Ohio and Mississippi rivers after escaping from the private fish farms. Then, in April 1994, high water flooded hatchery ponds at an aquaculture facility and carried the bighead carp into additional river systems.
"What we know right now is that they are in East Okoboji and Big Spirit, on the Minnesota-Iowa border," Doorenbos said. "We have not had any known samples in the Kanaranzi (Creek) or Rock (River), but it's very logical and in good probability that they could be."
Doorenbos said the bighead carp likely entered the local channels last spring.
"They start moving when you get a flood pulse, and last spring we had one heck of a flood pulse," Doorenbos said. "The Iowa DNR was under the assumption they had a pretty good barrier in the Little Sioux watershed, but the structure was leveled. Those fish which had been kept at bay bypassed and came up from the Missouri ... and got into Lower Gar. Once they get in there, that's the Iowa Great Lakes."
Samples taken nearly a year ago, on May 28, in the Iowa Great Lakes resulted in the capture of 55 silver carp and 82 bighead carp.
Why the concern?
Bighead carp are filter-feeding fish, meaning they feed on phytoplankton and zooplankton in lakes, rivers and streams. Doorenbos said they grow rapidly -- as much as a pound per day -- and can grow to 110 pounds. They also will jump out of the water, although not to the extent of the silver carp, which are often referred to as flying carp. There have been instances in which people have been hurt by carp jumping from the water.
The concern of the Minnesota DNR is not only for safety, but for the potential detrimental impact the invasives could have on our game fish populations.
"Our native, desirable fish, soon after they hatch they're looking for zooplankton to feed on," Doorenbos explained. "It's competition (for food)."
Okabena-Ocheda Watershed District Administrator Dan Livdahl said the district would rather take measures now to stop the spread of the invasives, rather than take a wait-and-see approach.
"Who knows what's next," Livdahl said. "We don't know what the effect of (invasive carp) will be in the Heron Lake Watershed District or the Okabena-Ocheda Watershed District, but whatever the results, we wouldn't like it."
Since discovery of both bighead and silver carp in the Iowa Great Lakes, the Iowa DNR has worked to raise money for an electronic fish barrier at the outlet to the Iowa Great Lakes, Doorenbos said. So far, it has about $600,000, and the structure is estimated to cost $700,000. The hope is to install the structure either this fall or next spring.
As for Minnesota DNR's plans to keep the invasive carp at bay, Doorenbos said it is looking at incorporating several new regulations. Among them are requiring boaters to pull their boat plugs before leaving a lake, and requiring anglers to dispose of live bait from their minnow buckets in the trash, rather than empty them in the lake. The latter precaution is recommended because the invasive carp minnows can easily be mistaken for other minnows used by anglers.
Doorenbos said there are also plans for the Minnesota and Iowa DNR to work together on fish barrier projects on border lakes, including Big Spirit and Loon lakes.
"The current hope is these guys won't be able to reproduce. They need a considerable amount of river miles for successful spawning," Doorenbos explained.
The invasive carp broadcast their eggs in the water column, but negative buoyancy would cause the eggs to sink. With positive buoyancy, the eggs float downstream, harden and hatch.
"There's no guarantee, but we're hopeful they won't be able to hatch in the Iowa Great Lakes," Doorenbos said.
In a meeting earlier this month of the Okabena-Ocheda Watershed District, Worthington Public Utilities Manager Scott Hain supported the closure of the east gate on Herlein-Boote Slough, even though it may mean less water flow into Lake Okabena, and less water to recharge the city's wells at Lake Bella, at the southern end of the watershed.
Hain said the establishment of the slough in the 1950s was thought to be a good source for water, but "it's certainly not the magic bullet people thought it might be."
According to Livdahl, the 247-acre wetland collects runoff from more than 5 square miles of agricultural land. When the diversion ditch was installed in 1983-1984, it cost nearly $168,000. The city of Worthington's share was more than $94,500, with the remainder of the bill paid by state and federal dollars and the Olson Trust, a local funding source.
Doorenbos said the DNR has been eliminating diversionary practices because "they don't function the way we thought they would work."
"At a time of low water, you're going to want more water, but the reality is there's no water to even divert to a diversion channel," he said. "In times of high water, people don't want the water."
Hain, Doorenbos and Livdahl all agree there is much yet to be discussed regarding the water in Herlein-Boote Slough and where it should be directed.
Livdahl said the gate that was closed could handle water flows of 60 cubic feet per second, while the west gate that remains open can handle only half that amount.
"The structure on (the west side) would need to be modified to take twice as much water," Livdahl said. "The consequence is the city (of Worthington) would never get water from the slough."
For now, Doorenbos said the east gate was closed because "we wanted to be able to say we took some action." He said what needs to happen next is a discussion between the DNR, the city of Worthington and all three watershed districts to work out a more permanent solution to the problem.
Daily Globe Reporter Julie Buntjer may be reached at 376-7330.