Pick your poison: Where to swim, and where not to swim in Iowa

There were many natural ‘lakes’ that were drained for farming after people of European descent arrived in Iowa. How many of these would’ve been defined as lakes (versus wetlands) by modern day limnology is anybody’s guess, but that number probably falls between a few dozen to a few hundred.

Limnology bins lakes into three main categories: oligotrophic (young, infertile), mesotrophic (middle aged, moderately fertile) and eutrophic (old, fertile). At the southern end of glacial extent across the Midwest, most of the glacial lakes would have already been considered eutrophic or near-eutrophic at the time of European settlement. Most of our natural glacial lakes in Iowa are shallow ‘dishpan’ systems (meaning that the basic contour of the bottom is saucer-shaped) that supported aquatic life throughout the water column. Now many or most of them are considered ‘hyper-eutrophic’, meaning their natural fertility has been overloaded with nutrients (nitrogen and phosphorus) from human activity. Long and short, since 1840 we’ve added thousands of years onto the age of our lakes. Indeed, many would not even be lakes any longer were it not for rescue efforts.

Iowa’s first constructed lake was Lake Wapello near Drakesville, finished in the early 1930s. There also was a fish hatchery constructed at the site where largemouth bass and other species were reared for stocking. Lake Wapello’s claim to fame for many years was that the state record largemouth was landed there.

The first batch of constructed lakes in Iowa also included Ahquabi (Warren County), MacBride (Johnson County), Backbone (Delaware County), Springbrook (Guthrie County), Pine (Hardin County), Morris (Lucas County), Lake of Three Fires (Taylor County), and Beeds Lake (Franklin County).

Constructed lakes are built by damming a stream, sometimes more than one stream, and the land use draining to the lake determines the quality of the water in the lake. When these first lakes were constructed, land use and Iowa farming were much more diverse than now. As diversified crop and livestock farming systems were bigfooted by corn/soy/CAFO, lake water quality in these constructed lakes suffered. The bigger the area draining to the lake, the worse the water tends to be. The flip side is that constructed lakes capturing water from a small watershed are much more vulnerable to drought stress.

As Memorial Day nears, many Iowans look forward to a day at a nearby beach. I can remember my folks taking us kids to Lake Ahquabi, along with a picnic lunch of sandwiches or cold fried chicken, way back in the day. Opportunities for a low-stress, low-cost mini-vacation for a family with young children are a wholesome, quality-of-life enhancement, a respite away from screens, stress and the modern non-stop compulsion to be “connected.” And you can’t beat beating the heat and humidity of an Iowa summer with a cool dip. Nothin’ makes the young-ins sleep at night like a day at the beach.

But if you’re reading this, I’m sure you know we have a perennial problem at our beaches and that problem is poor water quality. Immersing your body in a lake or stream is primally invigorating, an effect that lingers for several hours, right up until the moment your 8-year-old pukes onto your bed at 3 a.m. while you wonder if the potato salad went bad or if he swallowed some lake water.

Iowa DNR regularly monitors 39 state-owned beaches during the swimming season (May-Aug) for a variety of contaminants but of most interest are two: E. coli bacteria and microcystin. Microcystin is a toxin produced by cyanobacteria, commonly known as blue-green algae. Cyanobacteria were some of the first organisms on earth and helped create our oxygen-rich atmosphere. Think of them like this: they are bacteria with the capacity to undergo photosynthesis.

Cyanobacteria populations in a lake can increase explosively when conditions are right — warm water, lots of sunshine, and especially, lots of nitrogen and phosphorus. Iowa has it all, especially that last thing. Under some circumstances, cyanobacteria can produce toxic chemicals — cyanotoxins. Microcystin is one of many and the most commonly monitored in recreational waters. Microcystin can damage pretty much every type of cell in your body and both chronic (long term) and acute (short term) exposures are associated with a whole range of diseases. Cyanotoxins also seem to be particularly toxic to canines. Swimming in water that contains more than 8 ppb of microcystin is discouraged and Iowa DNR posts beaches with such signage when monitoring data exceeds that level.

E. coli are bacteria that live in the intestinal tract of vertebrates. You benefit from the E. coli in your gut. E. coli from sources outside your gut can cause disease in your body, but usually not. But sometimes. Some strains are highly toxic. E. coli is also very easy to detect and quantify in water and for all these reasons, it is an indicator bacteria, meaning its presence at certain levels indicates an increased risk, and that other more pathogenic organisms may be present. EPA has determined that people recreating in water containing less than 235 E. coli colonies (MPN or CFU) per 100 ml have less than a 36 in 1000 chance of becoming ill. This is the Beach Action Value and the threshold considered to be acceptable for Iowa beaches. Because E. coli populations can change rapidly in a lake, there are statistical methods that incorporate multiple samples to determine Beach Action Values, but I won’t dive into that weedy bay today.

Much has been made of the idea that E. coli in Iowa lakes can be sourced to wildlife, and especially geese, with the implication that this exonerates agriculture and especially the livestock industry for degraded water quality at our swimming beaches. Anyone can see that geese like beaches and may excrete their waste on or near the beach, and it stands to reason that they are a source of the bacteria. Hogs, cattle, and chickens, on the other hand, excrete their waste in CAFOs (usually) and E. coli-laden waste is uncommonly applied to cropped fields during the swimming season (May-Aug), and so how could this be a cause of impaired beaches, the Aggies sometimes ask. Some in our agencies and universities have been only too happy to explore this question, and it probably won’t surprise you that our ag establishment folks don’t object to this kind of water quality research.

A few things on that. We have been conducting a massive experiment over these past many decades whereby we’ve saturated a large percentage of our land with animal waste and thereby inoculated it with more E. coli bacteria than there are stars in the sky. Literally. One cow pie may contain more E. coli than there are people on earth. It’s a near certainty now that some E. coli can live and reproduce outside the gut because the conditions in our water are now not unlike the conditions in the gut of an animal — warm, organic rich, and especially, dark. E. coli perish rapidly when exposed to sunlight. The fact that so many of our lakes and streams are turbid (cloudy), sometimes from nutrient-driven cyanobacteria blooms, enables E. coli to endure. Whether the E. coli are from hog or geese or hummingbirds is almost beside the point, which is they encounter a hospitable environment when they get to our streams and lakes, and sometimes are able to take up residence. We call them an indicator organism for a reason — they indicate something is wrong.

So, where to swim? I looked at the Iowa DNR database for E. coli and microcystin over the past five years and our very best beach in terms of water quality is Triboji Beach at the far north end of West Lake Okoboji. It has never exceeded the E. coli or the microcystin standard over the past five years (2020-2024). Some of the other beaches at West Okoboji and the other nearby ‘Iowa Great Lakes’ do indeed exceed the E. coli standard with some frequency. This could be due to some urban runoff or old septic tank issues, as much of the area is highly developed. And don’t discount the possibility that the enormous amount of human traffic ‘ on’ the lake during the summer contributes significantly to E. coli levels. Only Crandall’s Beach at the far north end of Spirit Lake has exceeded the microcystin threshold over the past five years.

Lacey-Keosauqua Beach in southeast Iowa is probably second best for water quality — only two exceedences for E. coli and none for microcystin over the past five years.

The worst? One stands out — Lake Darling, without a doubt our worst lake for water quality. Water there exceeds the E. coli standard more than half the time, and the microcystin standard more than 35% of the time. The lake was restored in 2013 but restoration cannot and will not overcome nearby land use — enormous amounts of hog manure applied to the fields draining to the lake make it a cauldron of nutrients and pathogens that probably ought not ever see as much as a human pinkie toe dipped beneath its surface. I would not swim in Lake Darling — ever. Darling is the Floyd River of Iowa lakes, i.e. bad in almost every respect.

As the saying goes, pick your poison.

Former University of Iowa research engineer Chris Jones writes from Iowa and Wisconsin about the natural world and the intersection of agricultural and environment. He is the author of “The Swine Republic” and his work can be found online at https://substack.com/@riverraccoon, which is part of the Iowa Writer’s Collaborative.