Blue-green algae is probably the most prominent issue with aquatic vegetation that many Kansas lakes and reservoirs have dealt with, often making headlines when a new case of the toxic algae springs up. But another type of difficult-to-control vegetation rarely garners much attention from the media — Eurasian watermilfoil.
Labeled an invasive species of plant, the submerged vegetation forms a dense canopy at the surface of the water. It is commonly found in 1 to 15 feet of water, but can be as deep as 30 feet if the water is clear.
Lake Shawnee is one such area where Eurasian watermilfoil has flourished, leading the county to use herbicides in recent years to combat the spread of the weed.
“Our plan for Lake Shawnee has been to do a treatment of the full lake every several years with bump treatments in between to control the growth and spread of the watermilfoil,” said Mike McLaughlin, communications and public information supervisor for Shawnee County Parks and Recreation.
But despite being listed as “invasive,” Eurasian watermilfoil can actually be a beneficial plant in many ways to aquatic wildlife, providing food and shelter for several species. Predators like bass and walleye in particular use the weeds as cover.
“I have been an angler since 1948,” said iconic outdoors writer Ned Kehde, of Lawrence, “and across those many years and around the many waterways where I have pursued largemouth bass and smallmouth bass, I have found that Eurasian milfoil has been a godsend to those reservoirs that are blessed to have it growing upon its underwater terrains.”
To be frank, Kehde’s opinion on this issue carries water with a lot of anglers.Kehde, a forefather of finesse fishing — he is the namesake of the popular Ned Rig used by so many anglers today — has been an outspoken opponent of using herbicides to kill aquatic vegetation.
He became vocal about the issue when Douglas County decided to stop using the herbicide Ecomazapyr to kill vegetation after 20 trees died near the shoreline of Lone Star Lake, apparently of herbicide poisoning. However, the county continues to use another herbicide, Navigate, to control Eurasian milfoil.
Kehde spoke before Douglas County commissioners in July, saying he would prefer the county stop using the herbicide. Kehde told that commission that watermilfoil helps increase fish populations in lakes, and that some of his best fishing experiences have been at lakes where the plant grows, according to an article in the Lawrence Journal-World.
In Topeka, Kehde said he believes the introduction of herbicides to Lake Shawnee in past years has been detrimental to the bass populations, as well, and said mechanical or manual removal of excess weeds would be a better option.
“When the caretakers of Shawnee Lake deposited an invasive and toxic chemical into Lake Shawnee, they rationalized this poisoning by saying that they needed to rid the water of Eurasian milfoil,” Kehde said. “This bountiful and helpful aquatic vegetation was castigated as an invasive species even though it has been in the United States for more than a century. So, when is a species no longer invasive? For example, bluegrass is not native to the United States. House sparrows are not native. In fact, there are scores and scores of non-native species flourishing and relished by Americans.
“In fact, we have seen folks from the Kansas Department of Wildlife, Parks and Tourism stock grass carp into Gardner Lake, Kansas, and grass carp are not a native species. It looks as if this castigation is ill-informed and surrounded by prejudiced reasoning. I cannot understand why Eurasian milfoil is being poisoned.”
Shawnee County disagrees with the assessment that herbicides are the culprit, saying that while the bass population has indeed declined, it wasn’t related to the use of herbicides — at least not directly.
“We have a recollection that the decline in the bass population was evident before any treatments were done and that the decline was attributed to an illness,” McLaughlin said.
Kehde takes meticulous notes of all of his fishing expeditions, as he uses that information to give a quantitative assessment of his trips for the stories he writes about fishing. He said the decline in the bass population first began in 2010, with the population rebounding by 2015 before declining again after the lake was treated in 2016.
McLaughlin said the Eurasian watermilfoil first arrived in Lake Shawnee in 2011 and was treated in 2012 and 2016. A single treatment usually lasts three to four years, he said.
While the “invasive” label sounds menacing, some researchers are quick to point out that isn’t always the case.
It’s a complex issue. Even clearly harmful species such as Asian carp may offer some unexpected benefits, such as potentially controlling blue-green algae.
Zebra mussels are another prime example of invasive species where the end result of their presence may have both positive and negative consequences. In Lake Michigan, for example, zebra mussels infested the once-murky waters and had some interesting effects. The water became crystal clear — a welcome surprise for swimmers and beachgoers — as the super-powered mussels filtered the water at a much higher rate than other mussels.
For anglers, however, the clearer water was seen as a negative, especially as the base of the food chain — phytoplankton — was decimated in the process, leading state managers to scale back the annual stocks of predators such as king salmon. Clear water also causes vegetation to grow at a much higher rate as more sunlight filters down to the bottom of the lake.
However, in nearby Lake Erie, where zebra mussels are plentiful and the water is clear, the walleye population has unexpectedly boomed. The Cleveland Plain Dealer reported in July that after decades of boom and bust with the walleye population, the harvest of walleye in Lake Erie increased from 417,000 in 2011 to almost 2 million in 2018.
Depending on the layout of each lake, there is a careful cost-benefit analysis to each new species introduced in an ecosystem that must be carefully considered by wildlife officials. Because while the introduction of zebra mussels in Lake Erie has so far worked out, the walleye in Minnesota’s Lake Winnibigoshish reacted differently, with the larger fish thriving while smaller ones all but disappeared. And in nearby Mille Lacs Lake, a University of Minnesota study found that an explosion of zebra mussels in 2005 decimated the walleye population.
Kehde recommended people who want to know more about invasive species read “The New Wild: Why Invasive Species Will Be Nature’s Salvation,” by Fred Pearce.
“Here is hoping we can find a way to stop poisoning our waters and landscapes,” Kehde said. “The most effective and economical way to prune some of the aquatic and terrestrial vegetation is to do it manually.”
The county hasn’t scheduled a chemical treatment yet this year, but the Shawnee County Commission agenda shows the topic is set to be discussed at the next regularly scheduled board meeting, which takes place at 9 a.m. Monday in Room B-11 of the Shawnee County Courthouse, 200 S.E. 7th St. According to the agenda, Shawnee County Parks and Recreation will seek approval of a request to solicit bids at an estimated cost of $130,000, with funding from the 2019 operating budget.
The state, which helps manage the lake’s plants and wildlife, also has recommended chemical treatment, though a KDWPT biologist has said manual removal is possible with proper manpower.
“I did recommend controlling Eurasian watermilfoil (EWM), as it can become too abundant and can interfere with lake user activities, including swimming, boating, rowing and fishing,” said district fisheries biologist Richard Sanders, of Lawrence, who manages the fishery for the KDWPT as part of a Community Fisheries Assistance agreement with Shawnee County. “Since EWM can spread by fragmentation, mechanical control must also remove any cut EWM plant to keep from spreading the plant.
“An aquatic vegetation harvester might be an option. It would require a dedicated workforce to continue mowing and removing EWM periodically throughout the growing season. Application of an approved aquatic herbicide can provide some control (sometimes long-term with a whole lake treatment of fluridone) and is generally less labor intensive than mechanical control.”
Kehde said that during past applications, significant patches of American water willows were killed, as were burgeoning patches of American pondweed, coontail and bushy pondweed, which were not invasive species.
“In fact, these four species of aquatic vegetation are very important and much venerated plants, which help keep our reservoirs clean and help protect and propagate fish populations,” Kehde said.