In the early morning darkness of July 12, 2016, more than six inches of rain fell on Mora, Minn. and the surrounding area. This 1,000-year-rainfall washed out roads and sent local streams and rivers surging. The Snake River rose 12 feet in 24 hours.
Eventually the wall of water worked its way downstream, pushing the lower St. Croix River up a couple feet — and back into no-wake levels for another week.
Such freak rainstorms have pounded eastern Minnesota at least three times in the past five years. Similar storms have hit other parts of the St. Croix watershed, including northwest Wisconsin. In a few short hours, several inches of rain might fall on a small area.
Storms that hit the Snake River watershed garnered headlines on St. Croix 360 in July 2016, July 2018, and October 2019. Their increasing frequency is connected to global warming. The watershed today gets more rain on average each year, and is measurably warmer.
The Snake River, which runs for more than 100 miles through the region before joining the St. Croix River east of Pine City, has been the epicenter of several of these extreme rainfalls. The resulting high river flows can erode riverbanks and wash out gullies, dumping many tons of soil into the river.
The river has largely weathered the weather, though, thanks to lands and waters that continue to buffer the river. That’s according to a new report from the Minnesota Pollution Control Agency.
“This watershed is better able than many areas to absorb intense storm events, and the resulting high runoff and stream flows, because scientists consider it to still be ‘intact,’ meaning many natural areas have remained untouched, including wetlands and floodplains,” the report says.
Wild river, wide watershed
The Snake is a popular and storied river, offering wilderness and history, fishing and paddling, rocky rapids and placid pools.
It was called Ginebig-ziibi (anglicized as “Chengwatana”) by the Ojibwe people here when Europeans arrived, named for its abundant white pines. It was also the site of one of the first fur posts in the St. Croix River region, constructed by British fur traders in 1804 near present-day Pine City.
Today, some stretches are home to houses and cabins, other parts flow through small towns, while other sections go past farm fields — but much of the river remains surrounded by broad forests and bogs.
The landscape around any river determines how it handles sudden flooding and other threats to its clean water. Land and water is deeply connected. In the Snake’s case, more than 1,000 square miles that drain to the Snake.
Determining the health of a river requires careful study across this diverse region.
Water and wildlife
In 2006, scientists from the state agency in charge of measuring the health of Minnesota waters first visited different parts of the Snake’s watershed to systematically analyze its health. It was the first such river studied in a new systematic way that was rolled out across the state in the following years.
In addition to taking regular water samples to analyze for a variety of contaminants, they also conducted extensive examinations of the organisms that call the river home. Such “biological indicators” are often the best sign of river health, as many insects, fish, and other wildlife can only tolerate certain conditions.
In 2017 and 2018, agency scientists returned to the Snake to see what had changed in the past decade. They found that, while some stretches, and some lakes and streams that drain into the river, are contaminated with sediment, nutrients, bacteria and other pollutants, overall the region’s lakes and rivers remain healthy.
“Good water quality allows fish species that are sensitive to contaminants to thrive,” the MPCA says. “During the latest round of monitoring, MPCA’s crew captured a lake sturgeon, a sensitive species of concern in Minnesota — a good indication that the population is reproducing and well established in the river.”
Agency crews also found a variety of other sensitive species in the watershed, including northern hogsuckers and southern brook lamprey.
Precipitation and pondweed
In an era when climate change, invasive species, and runoff are threatening the Snake, its continued health is no accident.
The watershed in recent years has received on average two more inches of rain than the historical average going back to 1895. Average temperatures have increased by about one degree.
Non-native species are also encroaching. All the major lakes in the Snake River watershed now have a plant called curly-leaf pondweed. It can create dense mats at the water’s surface, inhibiting swimming, fishing, and boating, outcompete native plants, and can litter shorelines with dead plants after die-offs. It also provides poor habitat for native animals. Unfortunately, curly-leaf pondweed is expected to spread into the streams and rivers that connect the region’s lakes.
But the large amount of natural landscape in the watershed has helped the Snake survive.
“While the watershed has experienced changes in land use and increased urbanization, many natural areas have remained untouched, helping to prevent additional impairments,” writes the MPCA. “In spite of all these possible stressors, the watershed has remained relatively stable, with few new impairments.”
The MPCA report notes that landowners have implemented hundreds of projects across the watershed to help protect water quality, but more is needed to actually improve some impaired lakes and streams.
Each year on the first Saturday of May, the Snake River Canoe Race sees 100 or more watercraft descend 14 miles of the river, ending in Mora. It’s a draw for hardcore racers in skinny Kevlar boats, and others who participate in the very competitive aluminum canoe class.
Some participants just do it to celebrate the start of the spring paddling season, when the trees are just beginning to bud. The Snake River twists through forests and farms, with many riverside residents standing around bonfires on the bank, cheering on the paddlers.
Some years, the water flows are too low and the race is moved to a nearby lake. Other years, it is a raging torrent that demands caution. The race route includes exciting rapids and peaceful pools. The banks are often exploding with migrating birds and some years, bright white trilliums and trout lilies blanket the forest floor.
Paddlers can’t really be blamed for getting distracted from the finish line to study this scenic and healthy waterway.