HAMILTON COUNTY, Iowa — It’s a beautiful night on Little Wall Lake. It’s clear that our rainy spring has temporarily solved its biggest problem: low water levels. But around here, each solution seems to expose another problem.
“Some lakes in Iowa are a lot easier to manage–they almost manage themselves,” says Iowa DNR lake restoration coordinator, Mike McGhee.
“Unfortunately, Little Wall Lake is one of those lakes that’s going to take a lot of management.”
Iowa’s southernmost natural lake is a foot deeper than last year, but the quality of the water seems worse than ever.
“I don’t want to swim in it,” says Jeff Knutson. “As you can see, it’s not very clear.”
Knutson lives on the lake and says the DNR is to blame.
“Part of the problem there is, they have overstocked the grass carp numbers.”
The DNR doesn’t disagree.
When they stocked grass carp in the early 90s, grass carp were widely considered to be the perfect solution for lake weeds. They grew fast, didn’t naturally reproduce, and had a life-expectancy of only five to ten years. Since then, the carp have proven to be much longer lived than originally thought. In fact, many of Little Wall Lake’s original carp are still alive and nearing 25 years old.
The carp did deliver on one promise though: they did a real number on Little Wall’s aquatic vegetation.
“They did such a good job, they’ve eliminated it,” McGhee says, “and one of the by-products to using grass carp–it can contribute adversely to water quality.”
Aquatic vegetation filters out silt and nutrients from lake water and harbors micro-organisms which do more of the same. Without it, the nutrients suspend in the water and promote unsightly and sometimes unsanitary algal blooms.
The best way to improve water quality would be to eliminate the grass carp using chemicals, but again, more problems. That would kill sport fish like walleye and bring back the weeds; two things no one wants.
“They had the fish-kill in Black Hawk (Lake in Sac County),” says resident, Jane Todey, “and they’re experiencing the same problem we had (thick weeds). I don’t know why it should be any different for us should they go ahead with those plans.”
Despite the doubts of the residents, the DNR says they will be involved in the plan but that it will likely involve a fish kill to reset the lake’s ecosystem and eventually an expensive weed harvester to cut the weeds out of the lake each year.
“Get a better fishery in the system there and then we’re gonna have to be aggressive about aquatic vegetation control,” says McGhee, “and that can be done with harvesting, or chemicals or probably a combination of both. But it’s not something you do once and fix, it’s an ongoing operation and maintenance cost.”
Residents say they just want to be involved in the search for a solution, even if this challenging lake has no final one.
“They’re the experts,” says Todey. “We need their expertise to help us figure out solutions for this lake that will work.”