Mysterious creatures of the St. Croix River

“Gabe found some kind of dead animal in the water,” my son says casually, as he wades past me and back to his paddleboard.

Now, most people would probably shrug and move on, but I instead ask, “Did it smell bad? What does it look like?” When he tells me that it merely looks gross, but in fact has no smell, my curiosity is even further piqued. By now, I’m tromping through the water, heading down the shoreline to investigate for myself. Sure enough! A moment later, I’m gazing down at a gelatinous blob in the St. Croix River, which is a living version of an animal I’ve only ever seen as a fossil.


Have you ever seen something like this in the water? #stcroixriver #nature #weirdanimals

♬ original sound – Angie Hong

Bryozoans are microscopic aquatic invertebrates that live in colonies and build exoskeletons similar to those of coral. In some species, their colonies can look like antlers, moss, or furry vines that spread across rocks. If you find one in the St. Croix River, however, it’s more likely to look like a giant glob of snot.

Worldwide, bryozoans are found on every continent except Antarctica, though only 70 of the 8000 known bryozoan species live in freshwater. Like mussels, they are filter feeders that eat diatoms and other microscopic organisms, and their presence usually indicates good water quality.

Bryozoans are just one of the many strange and unique animals that call the St. Croix River home. Only a week earlier, the boys had texted me a photo of a giant, frowning fish they had caught in the river, which turned out to be a golden redhorse. This native fish species is intolerant of pollution and usually only lives in rivers and streams. 

A golden redhorse caught from the St Croix River in downtown Stillwater. Considered by many to be a “rough fish,” these are actually native fish that are usually only found in rivers and streams with relatively good water quality.

More than 60 species of fish call the St. Croix River home, including everything from American eel to sturgeon, paddlefish, and giant flathead catfish. “Be prepared for anything,” advises the Minnesota Department of Natural Resources. In addition, the St. Croix River is home to 41 species of native freshwater mussels, making it one of the most diverse and populous assemblages of mussels in the United States.

During our two-hour paddle from Log Cabin Landing to Marine, the boys and I found numerous mussels in the shallow waters of the St. Croix River, tracing lazy circles in the sand. Their paths are like the doodles of a toddler, with looping lines, lopsided circles, and meandering itineraries. The catalog of St. Croix River residents includes 17 state-listed and five federally-listed threatened and endangered mussel species.

Above: A freshwater mussel creates art in the river bottom; Charlie and Gabe paddle on the St. Croix River; a frog hangs out in the shallow water of a sandbar.

Along with bryozoans, paddlefish, and freshwater mussels, the St. Croix River also supports a vast array of pollinators, birds, reptiles, amphibians, and mammals. There are otters and foxes, softshell turtles, great blue herons, and monarch butterflies. Thanks to protections established by the Wild and Scenic Rivers Act, trees grow tall along the river’s banks, creating a vibrant corridor of life. These protections also make it possible for people to enjoy boating and paddling on the river without seeing houses, roads, and other signs of development.

Along the St. Croix National Scenic Riverway, it is possible to canoe, kayak or ride a standup paddleboard without seeing roads, houses or other signs of development.

Last week’s adventure on the St. Croix River ended as most good river journeys do, with plans to do it again. Before we’d even pulled the paddleboards ashore, we were already discussing our next itinerary and planning provisions to bring. With 169 miles of scenic beauty, the St. Croix River offers opportunities for easy day trips, week long excursions, and everything in between.

To learn more about the St. Croix River or download river maps, visit

Join a guided tour with Wild Rivers Conservancy of the St. Croix and Namekagon on Aug. 14, 10:30am-1pm near Minnesota Interstate State Park. Learn why the St. Croix is one of the best places in the world for mussels to thrive on this educational paddle led by Outdoor Educator Amy and National Park Service Ranger Marian: