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HomeLand & Water​Healthy Stream, Healthy Trout

Healthy Stream, Healthy Trout

By John Weiss, January 24, 2024

Canfield Creek, a small trout stream in Forestville/Mystery Cave State Park, joins the South Branch Root River. Are neonicotinoids killing invertebrates, the canary in the coalmine for stream health? (Photos by John Weiss)

Healthy Stream, Healthy Trout


This article was  first published by the Rochester Post-Bulletin in October 2023. It is republished as part of Root River Current’s continuing coverage of water quality issues in karst country. 

FORESTVILLE — Canfield Creek drifted in front of me, quiet, clear, a bit high from recent rains. Several brown trout, one maybe in the mid-teens, flexed in the soft current.

For decades, that stream in Forestville/Mystery Cave State Park has lured me with its beauty and those trout have eluded me with their wiles. This past fall, however, I saw Canfield in a new way because I’ve learned that neonicotinoids—a class of pesticide often referred to as neonics—are increasing in many of our waters, possibly killing our water bugs and therefore, hurting our fish. Other problems, such as nitrates and turbidity, continue to vex us.

Those are not meaningless things to know. Water quality tells us what the streams are like, which in turn indicates what the surrounding land use is like and, finally, what we are like because we determine our water’s fate.

My research began when I watched a state team collect invertebrates (bugs), such as mayflies and caddis flies, in Canfield Creek, near its twin Forestville Creek, for a report on some sentinel streams as an indicator of what so many other similar streams are like. That got me thinking more about our water. 

I wrote earlier about the massive amount of data now available from similar crews across the region. It gave me hope because we have the data. The next question was what are the data saying? That offered much less hope.

Saying they are better or worse is exasperating because water quality is maddeningly hard to pin down. Water changes from day to day, year to year, while pollutant levels, fish numbers, all fluctuate. It takes years, even decades, to clearly show trends. The best I can conclude is that new and old problems continue but a few things have improved.

Pollutant maps of the Zumbro, Root and Whitewater watersheds all show a dismaying number of impaired stretches, many with multiple woes. For example, South Fork Zumbro coming out of Rochester is impaired for nutrients, turbidity and fish. More agricultural areas have a greater chance at turbidity, poor bugs and bacteria while Wabasha County is mostly impaired for bacteria. New testing is underway and I’m hoping water will look better but I’m not hopeful.

Further clouding water’s future is climate change

“Climate change has the potential to deteriorate the effectiveness of these biological indicators by disrupting their response to watershed-scale disturbances such as impervious surfaces, agricultural runoff, hydrologic alteration, and erosion,” according to the Minnesota Pollution Control Agency.

To add to water woes, the agency says: “chemical pollutants, agricultural runoff, hydrologic alterations such as stream bed alterations and damming, and other human activities have cumulative effects on biological communities over time.”

My research also came in part because over the past few years, I’ve found evidence that there are fewer of the bugs like mayflies, caddis and crane flies that are so vital to our streams and rivers. The Minnesota Pollution Control Agency says those bugs are often better indicators of stream health than chemical analysis alone. The agency regularly tests our waters for bugs but only for what kind, not hard numbers because those numbers are extremely difficult to find.

The National Weather Service, however, which for years has been documenting the huge hatches of larger mayflies on the Mississippi River, says the hatches have dropped by about 50-percent in the last decade or so. And about a dozen avid trout angler friends have been saying for years that hatches are way down. 

“There was a tremendous drop this spring,” said one fisherman. “The lack of mayfly hatches was noticeable.”

One of the ways to find out how healthy a trout stream is looking for bugs such as this Cased Caddis that was in Canfield Creek.

They also aren’t seeing masses of insects on their windshields as they once did; those masses are ugly and streak windshields but they do indicate good water.

I’m not alone in wondering. Dr. Neal Mundahl, a Winona State University expert on bugs and streams wrote in a recent Minnesota Trout Unlimited magazine:

“In my 30+ years of monitoring stream communities in southeastern Minnesota, I’ve wondered why different types of stoneflies, mayflies, amphipods, and even snails seem to have vanished from some streams where they used to be abundant.

“We all might be noticing some local examples,” he said, “of what is becoming a widespread phenomenon: a decline in aquatic invertebrates, especially insects, possibly caused by the largest group of insecticides currently on the global market.”

He is referring to neonics.

Perhaps not perfect evidence but enough to make me wonder—and worry

According to the Xerces Society, which promotes invertebrate conservation, “Neonicotinoid insecticides are now the most widely used class of insecticides in the world. While they were initially introduced as less harmful than older insecticides, research has now shown their devastating ecological impacts. Neonicotinoids are very toxic to pollinators, beneficial insects and aquatic invertebrates.”

The Minnesota Department of Agriculture (MDA) also sees potential problems with them. Two of the five kinds of neonics—clothianidin and imidacloprid—are now on the state’s list of five surface water pesticides of concern. The five made up 95 to 97 percent of pesticides detected over reference values, according to the MDA’s 2022 Water Quality Monitoring Report.

One of them, clothianidin, shows up most in southeast Minnesota—49 percent in one test, 61 percent in another; imidacloroprid shows up most in urban areas because it’s used in so many household pest killers. A 2022 study in the Root River watershed found clothianidin in all 19 samples; 18 were above the federal chronic benchmark. They are found in tiny amounts, parts per trillion.

“The federal Environmental Protection Agency has set benchmarks for them,” said Dave Tollefson, Surface Water Monitoring Unit supervisor in Rochester in the Pesticide and Fertilizer Management Division.

Benchmarks are conservative and try to set levels that will not pose an unreasonable risk to aquatic life. It has benchmarks for chronic exposure, which is longer-term, and they are lower—while acute ones, that can do damage or kill right away, are much higher. Benchmarks can help us interpret the data, but a Minnesota specific water quality standard would be necessary to determine if a waterbody violated the Clean Water Act.

Those chemicals can break down quickly so “what we find in the river came from application recently,” he said. We should watch for those kinds of chemicals because “insecticides are by far the most toxic,” he said. “They are an insecticide and insecticides aren’t selective on good and bad bugs so there is a higher risk.”

Interestingly, the EPA lowered that chronic clothianidin benchmark about six years ago from 1,100 parts per trillion (ppt) to 50 ppt, he said. “It muddies the water in terms of long-term data sets,” he said.

Because of what the MDA was seeing in the mid-part of the past decade, it began to monitor more in agricultural areas, “after which, higher detection frequencies were observed,” it said.

But the department data show the percent of clothianidin samples tested above the federal chronic benchmark has risen dramatically in the past several years (except 2021 that was a drought year). Nearly all of them were found after storms. None were found over the federal acute benchmark for invertebrates.

Regulating neonics, other pesticide standards

The MDA has the authority to regulate pesticides in the state, including the neonics. However, pesticide-treated seeds are not considered pesticides, but rather treated articles, which are regulated by the EPA.

Some seed gets treated with pesticides in Minnesota; in these cases the MDA regulates the pesticide up to the point at which it coats the seed. Other seeds are treated outstate and later planted in Minnesota. The MDA estimates that the amount of neonics used for seed treatment exceeds all other uses in the state.

The MDA meets annually to share monitoring results with the MPCA, which is responsible for developing and enforcing water quality standards to protect aquatic life. The MPCA has noted the need for the neonicotinoid water quality standards, but other chemicals, including polyfluoroalkyl substances, also known as “forever chemicals,” have a higher priority.

Nitrates are another pollutant I’ve been watching for decades because they can be really bad in drinking water and might be a stressor in streams and rivers. They are also seen as a good indicator chemical, telling us that if they are in the water, there’s a good chance other pollutants are with them.

Just how bad they are isn’t perfectly understood, according to Michael Rafferty, MPCA communications manager. “It is likely that in fish (and other vertebrates) nitrate reduces the efficiency that oxygen is carried in the blood,” he said.

Sampling for nitrates

For about 20 years, I’ve taken water samples from the South Branch Middle Fork Zumbro River to the Olmsted County lab where they are tested for nitrates and other parameters. Several years ago, I would have said conclusively that things were looking bleak. In the first several years, the levels only exceeded the 10 parts per million standard once, about 10.2.

But several years ago, they were spiking well past 20 ppm and they once averaged above 10 ppm for a year. In the past few years, maybe because of drought, maybe because of more careful farming, they seem to be lower. Again, a few readings, or even a year’s readings, don’t tell the whole picture.

Even after rain, 2023 levels were around 1.1 to 1.8 ppm. Caitlin Meyer, Olmsted County water resources coordinator, said “nitrate is typically at its lowest this time of the year… Due to the drought, most of the streams in southeast Minnesota have been baseflow dominated for a large portion of the summer.”

These brown trout, some more than a foot long, were waiting for food to come down a riffle in Canfield Creek. A healthy stream means healthy trout.

But there is another thing to consider, not just parts per million, she said—total amount going downriver. In high water times, nitrate levels are often lower because they are diluted but when you factor in heavier flow, total nitrates can be higher. “The flow rated totals are the larger picture of the total load moving downstream,” she said.

The big question is if we’re getting better. Again, it’s not an easy answer but Meyer said. “the latest trend report for the Zumbro as a whole, shows a slight decrease in the nitrate concentration to tributary rivers within the last 5-15 years. We’ll know more after this round of intensive monitoring.”

The Department of Agriculture, however, says this region is the worst for nitrates in Minnesota. Its testing found nitrates in every sample from both base and storm flow in the Southeast. We also had the greatest median concentration at 8.26 ppm in base flow.

Because of problems with nitrates both in the state and in the Gulf of Mexico where they cause a major algae problem, leading to a massive dead zone, Minnesota is considering lowering the acceptable chronic level of nitrates in cold-water streams and lakes to 5 ppm and 8 ppm for warm-water lakes and streams. The one for acute levels would be 65 ppm.

TSS—Total Suspended Solids

Finally, turbidity in our waters, formally known as total suspended solids, or TSS, is really a problem. This past summer, even with the drought, the Zumbro where I sample, never got really clear. But then, some rivers just don’t clear up perfectly, Tollefson said.

The crazy part is how visibility readings can vary. After heavy rains, the reading at Oxbow was a mediocre 28 centimeters (about 11 inches); several miles downriver, it was a bad 7 cm (about three inches). Why such a difference, I don’t know.

That silt doesn’t just look bad, it’s also hurting the river and any other river or stream with a heavy load. A study of conditions for fish in the Zumbro watershed, along with the Root and Whitewater watersheds, found turbidity averaged 89 percent good to fair/good. The same one for invertebrates found only 56 percent good to fair/good.

The difference is probably that silt covers the riffles where the invertebrates live. Fish can get along with other sources of food not raised in riffles but the wider their food base, the better.

For this parameter, I found some hope because one study found TSS dropping. My guess was that the law requiring landowners to leave 16.5 feet of vegetative cover along ditches or streams and 50 feet along lakes has been helpful. No study has been done to prove my hunch but “that is one theory a reader could come back with,” said Jordan Donatell, MPCA Supervisor of the South Biological Monitoring Unit.

There’s hope

Here are some other upbeat pieces of news: Water monitoring data show a decreasing trend in phosphorus and sediment from runoff. Trout streams are in good condition overall despite the chemicals.

Furthermore, from 1973 to 2008, turbidity, phosphorus, ammonia and biochemical oxygen demand (a measure of stuff in waters that take up oxygen), all dropped dramatically. Since then, however, only turbidity continued to improve.

With climate change comes more rain and snow, which can flood our waters, but also adds to the groundwater levels that then gush or seep out as springs to feed more streams. With the streams come more trout.

While some things might be looking better, it doesn’t necessarily mean our waters will be improving right away. “It’s not an overnight process to improve … things that ail our water quality,” Donatell said.


Learn more about regional water quality issues in these Root River Current articles:

▪ Minnesota’s 2024 Plans for Addressing Nitrate Contamination in karst country
▪ Local Forums, EPA Raise Questions about SE Minnesota water quality
▪What Happens When Feedlots Get Bigger in Karst Country?
▪ Water: A Resource In Crisis
▪DNR shocks trout to check health of area streams
▪ Root Causes, Root Solutions
▪Walk The Walk And Talk The Talk, Too

Related stories can also be found on the Land & Water topics page.



John Weiss was a full-time reporter for the Rochester Post-Bulletin for 41 years and wrote the Back Roads column for more than 10 years. His passions include hunting, fishing, birding, nature photography, hiking and just kicking around.

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