If you’ve grabbed a bite to eat at the Brookside Bar and Grill in Marine on St. Croix, you’ve probably noticed that the restaurant has a unique claim to fame; a stream runs right through the middle of the building! The Mill Stream originates in William O’Brien State Park and flows downhill, across Hwy 95, and through the Brookside, before cascading down a waterfall to the St. Croix River. This tiny stream gave rise to the first commercial saw mill on the St. Croix River and now attracts history buffs and nature lovers from around the state. 

During Marine’s Art & Nature camp this summer, I led a group of grade-school aged children on a nature scavenger hunt that included searching for aquatic macroinvertebrates and other critters in the Mill Stream and St. Croix River (macro – meaning you can see them with your eyes; invertebrate – meaning they have no internal skeletons). During an hour of muddy, sloppy fun, the kids discovered a wide assortment of mussels, frogs, leeches and insect larva, including species like caddisfly larva and hexagenia mayfly nymphs (giant burrowing mayfly) that are only found in high quality, clean streams.

Scientists conduct macroinvertebrate surveys on streams to create “Index of Biological Integrity” (IBI) scores that function much like grades on a report card. According to Mike Isensee, Administrator for the Carnelian-Marine-St. Croix Watershed District, Mill Stream will likely get an IBI score of “B” in 2022. However, the district hopes that water quality improvement efforts will bring that grade up to an “A” over the next decade. 

This fall, the district is finishing up work on a multi-stage Village Center Revitalization project, completed in partnership with the City of Marine on St. Croix. The project includes two new stormwater basins, a pre-treatment basin, and two wetland restoration projects, constructed to treat polluted runoff from Hwy 95 before it flows into Mill Stream. Together with gully and ravine stabilizations in town, the retrofits are expected to keep an estimated 22-27 pounds per year of phosphorus out of Mill Stream and the St. Croix River.  

The Marine Village Revitalization project has benefitted from a $224,000 U.S. EPA 319 grant and a $97,600 Minnesota Clean Water grant, awarded to Carnelian-Marine-St. Croix Watershed District.

During a recent presentation to the Washington County Water Consortium, Isensee talked about the high level of partnership between the city, watershed district and other governmental partners that has allowed this project to move forward seamlessly. Community volunteers have also been integral. “We’ve had four planting events so far, and volunteers have planted roughly 8000 plants,” says Isensee. 

The district will also be engaging student volunteers to continue monitoring macroinvertebrate populations. This coming year, high school biology students from St. Croix Prep will work with Washington Conservation District staff to collect and analyze aquatic macroinvertebrates in Mill Stream as part of a volunteer stream monitoring program. With hope, these populations will continue to flourish as water quality in the stream improves. 

This Saturday, Sept. 11, 9-11am, Carnelian-Marine-St. Croix Watershed District and Washington Conservation District are seeking volunteers to finish planting a large raingarden and stormwater channel constructed as part of the Marine stormwater retrofit project. To volunteer, simply meet at the gazebo in Marine on St. Croix (kitty-corner from the General Store) at 9am. Bring gloves, rubber boots, a water bottle, sunscreen and bug repellent, and gardening tools (if you have them). For more information, contact mike.isensee@cmscwd.org


Angie Hong is an educator for East Metro Water, a local government partnership with 25 members - www.mnwcd.org/emwrep. Contact her at 952-261-9599 or angie.hong@mnwcd.org  or follow her on TikTok @mnnature_awesomeness.

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