The St. Croix River is sometimes called the Mississippi River’s “cleanest tributary.” That’s hard to define, but one look at their confluence illustrates that they are very different rivers. The St. Croix’s water runs blue and clear, while the Mississippi is brown and muddy.

Dan Lunzer, an FAA-certified drone pilot who operates aerial photography and video business Great North Drones, recently shared a 20-second timelapse of the confluence (it shows 20 minutes in real time).

The footage shows the blue and the brown mingling together, as well as boats navigating between the two rivers. It puts in stark juxtaposition the differences in water quality between the two.

But it doesn’t tell the whole story.

Sources of sediment to the Mississippi River above the St. Croix in average conditions:

There are about 530 miles of the Mississippi River before it is joined by the St. Croix. Most of those miles it too appears clean and clear. But 30 miles above the St. Croix, the Minnesota River flows into the Mississippi.

When the Minnesota meets the Mississippi, it looks much like when the St. Croix joins.

The Minnesota River is what carries most of the sediment visible in the Mississippi-St. Croix confluence. Most of the Minnesota flows through corn and soybean farm country in the southern and western regions of the state. It also flows through loose glacial material that easily erodes.

Minneapolis-based painter Greg Lecker recently portrayed the Minnesota-Mississippi confluence in a painting called “Mixing,” seen in the gallery above. He donated it to the St. Croix Watershed Research Station, which has studied water in all three rivers extensively.

The St. Croix and upper Mississippi have their share of water quality challenges, but both carry far less sediment. They also both flow partly through forested landscapes without as much intensive agriculture or erodible soils.

There’s another critical difference for the St. Croix: bank buffers.

“The St. Croix is cleaner because it has been protected by the Wild and Scenic Rivers Act for over 50 years, with the majority of the 255 miles of shoreline still in a natural state,” said Deb Ryun of the St. Croix River Association.

Ultimately, the reasons two rivers can look so different is more complicated than it first appears.

Learn what you can do to help Minnesota’s rivers.

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