Swimming below the surface of the St. Croix and its many tributaries are numerous unseen creatures, from aquatic insects to crustaceans, from algae to fish. Work last year by a retired biologist has revealed a little more about the fish that call this region’s waters home. Konrad Schmidt recently shared his annual report with the various government agencies that oversee his work, and it contains a lot of interesting information.

Schmidt conducted surveys and sampling across Minnesota and some of Wisconsin last year, looking for species from the Boundary Waters in the north to the Root River in the south. He focuses on lesser known species — minnows, darters, shiners, and kin — and not just walleye, bass, or muskie. Too small for most people to notice, and not pursued by anglers, Schmidt has documented these little fish in detail. The ichthyologist spent most of his career working for the Minnesota Department of Natural Resources on non-game fish projects, until retiring in 2009. He continues several projects on his own time, under special permits with the DNR and often in close collaboration with current staff.

Hiking small streams with a backpack electrofisher, or canoeing and boating larger waters, or using hook-and-line, or a net, Schmidt and his accomplices seek to better understand obscure fish, their hidden lives, and the watery worlds they call home.

His efforts in 2023 included a few special projects in the St. Croix basin: backwater lakes on the lower river, spring-fed creeks that feed the St. Croix, rivers threatened by proposed hog farms, and more. He and his team by chance found three specimens of one unique species, the American paddlefish, dozens of miles farther upstream on the St. Croix than it has previously been documented.

Paddlefish surprise

One day last May, near the Dalles of the St. Croix, Schmidt was following a DNR boat that was electrofishing for mooneye as part of an unrelated study related to endangered mussels, using a low-level electrical charge in the river to temporarily stun fish. Among the species they were seeking, three big paddlefish floated to the surface.

These relatives of the sturgeon have what look like giant noses called rostrums, which seem to smell electricity rather than odors. Paddlefish are basically blind, but their heads and rostrums are covered in tens of thousands of receptors that detect weak electrical fields, similar to those found in some species of sharks and rays.

The electrical fields these sensors detect are created by the zooplankton they feed on. The sense is believed to be so precise that it’s capable of pinpointing individual organisms nearly invisible to the naked human eye. When a swarm is located, the paddlefish swims through with its mouth gaping open, filtering water and devouring the micro critters.

Schmidt says he has a long history with paddlefish. In 2000, he started a study funded by the U.S. Fish and Wildlife Service to survey paddlefish in the Mississippi River. Over the next few years, he and his crew captured, measured, tagged, and released more than 1,800 of the fish.

To the best of Schmidt’s knowledge, no paddlefish has been previously documented in the St. Croix above Stillwater. He said all three they observed “appeared healthy and recovered rapidly,” before being placed back in the river.

Paddlefish are designated as “threatened” by the state of Minnesota, primarily because of habitat destruction. Dams are a big obstacle to their spawning and migration, while boat strikes are also a concern. Schmidt’s find last spring extends the known range of paddlefish in Minnesota 27 miles up the St. Croix.

Spring creeks

The lower reaches of several tributaries to the lower St. Croix River, primarily small spring-fed creeks but also including the Apple and Kinnickinnic Rivers, offer unique habitat. Schmidt sampled a dozen of them last year, and says that these lower reaches, which are connected to the main stem of the St. Croix below barrier falls or other obstacles, usually offer colder, clearer water than the main river, and can support unique species.

Schmidt and his partners sampled streams from Taylors Falls down to River Falls. They identified 58 species of fish among all the streams. The most diversity was found on the upriver end, in Lawrence Creek with 32 species, the middle of the stretch, the Apple River with 29 species, and on the downstream end, the Kinnickinnic with 28 species.

All told, Schmidt and company survey 12 spring creeks and found 58 fish species. Rare species included the Gilt Darter, Mud Darter, Fantail Darter, Largescale Stonerollers, and the American Brook Lamprey.

Brook trout minnows from St. Croix River spring creek. (Konrad Schmidt)

The spring-fed creeks are also known as a refuge of the enigmatic brook trout, the only native trout species in the region. Schmidt observed a drastic decline in brook trout this year, compared to the count when he sampled the streams more than 20 years ago.

In Gilbertson Creek in Scandia, which spills into the St. Croix at Log House Landing, Schmidt says he caught 120 brook trout when sampling in 2000. This year, he found none. A few miles down the St. Croix, in Spring Creek in May Township, Schmidt counted 118 brook trout in 2000. This year, he caught about 10.

“This decline could be the result of the chronic drought that this part of the state has experienced in recent years,” he theorized. “However, stream temperatures may have exceeded what Brook Trout can tolerate due to climate change.”

Hog water

It’s hard to protect what you don’t know exists. That’s why, when a new pollution threat emerges, it’s important to survey downstream waterways before changes begin, setting a baseline. If something changes in the future, fish might be the first indication.

So, last year Schmidt and his crew surveyed the Wood and Trade Rivers. Those two tributaries flow through the area proposed for a new Concentrated Animal Feeding Operation (CAFO), also known as a factory farm, that would house about 20,000 hogs and produce seven million gallons of manure each year to be spread on surrounding fields.

With spreading fields located on the banks of the Wood, Trade, and other streams, and the industry’s track record of runoff, the basic ecology of these rivers is at risk. Manure runoff at another CAFO in the St. Croix watershed in 2019 killed numerous fish in a Willow River tributary.

In the Trade and Wood Rivers, Schmidt found a rich array of fish life, with 47 species, including the imperiled Gilt Darter.

“Overall, both streams appeared healthy exhibiting good water quality, holding diverse fish communities, and generally having wide, undisturbed, woody riparian zones,” he reported.

The streams in question primarily flow through very sandy country, which may be why there were not high numbers of any species. Sand doesn’t hold much in the way of nutrients, Schmidt explains, which means the rivers would not be very “productive.” It also could mean they would be more easily affected by even small amounts of pollution.

”Naturally occurring low productivity is always better than nutrient enrichment and high (hyper-eutrophic) productivity caused by of manure spills or by land application of manure on adjacent croplands in these watersheds,” he writes.

The most recent CAFO proposal in the area called for spreading about 7 million gallons of manure on surrounding farm fields each year. While intended to fertilize crops, much of the nutrients can run off into nearby waterways.

Range restoration

(Konrad Schmidt)

Over the past century, many lakes and streams in Minnesota took a beating from pollution, agriculture, erosion and other human impacts. This degradation forced out a lot of fish, as species that require the cleanest, clearest conditions disappeared. Types of shiners, darters, and other sensitive minnows could not survive in water fouled by sediment or algae or any number of other contaminants.

But Schmidt points out that, today, several such lakes have been restored to something like their historic conditions. Shoreline vegetation was replanted, storm runoff rerouted, streams cleaned up. The water has responded, with algae blooms reduced, clarity increased, and the underwater vegetation needed by many minnows has returned. But fragile fish are still gone.

There are a few Twin Cities area lakes that Schmidt says once hosted — and lost — diverse minnow species, and may once again be suitable for the fish. But it’s easier to drive a fish to extinction than create a self-sustaining population from scratch. Schmidt and his partners have been trying to bring some special species back to a handful of lakes for the last few years, including a couple in the St. Croix River basin.

The effort began with relocating five fish species from a lake in Le Seuer County to two Twin Cities area lakes: Lake Phalen (in the Mississippi River watershed) and Lake Elmo (in the St. Croix watershed). Lake Elmo was the more successful of those two, with several species showing a growing population, while Phalen still suffers from storm sewer runoff. Thanks to the restoration work, Lake Elmo is now home to Blacknose and Blackchin Shiners, Banded Killifish, Least Darters, and Pugnose Shiners.

The translocation initiative has since expanded to include some other work on St. Croix lakes, including Big Carnelian, Big Marine, and Square Lakes. Last year, Big Marine Lake supplied nearly 600 minnows — Blackchin Shiner, Blacknose Shiner, and Banded Killifish — for transport to Bde Maka Ska, in Minneapolis.

Also last year, Schmidt for the first time attempted translocating northern sunfish to Square Lake. Northern Sunfish are a species of special concern in Minnesota, and currently found in just 84 lakes and seven streams.