Researchers drive a wakeboat through a designated testing area on surfing mode.
Fishing? For sure. Water skiing? Yes, please. Taking in the beauty of the water from the dock? You betcha.
Many Minnesotans revere our 10,000 lakes for their calm, clean waters and recreational opportunities. But when powerboats kick up sediment from the lakebeds, the disruption in the water can lead to harmful algal blooms that not only turn the surface water green and grimy but also threaten the health of the delicate ecosystem below, according to a University of Minnesota study.
Researchers tested seven recreational powerboats commonly used in Minnesota lakes and rivers based on their two most-used settings. For non-wakeboats, this is displacement mode/leisure cruise and planing mode/cruising; for wakeboats, it’s semi-displacement mode/surfing and cruising.
The study found that all powerboats produce water currents and turbulence that can disturb the lakebed below. The more powerful turbulence from wakeboats can directly resuspend sediments in the water.
Image courtesy of St. Anthony Falls Laboratory, University of Minnesota
What’s the harm?
Disrupting the lakebed can cause a host of issues for lake environments, explains researcher Jeff Marr, associate director of engineering and facilities at the St. Anthony Falls Laboratory in the University of Minnesota College of Science and Engineering. Fish are visual feeders, so it’s hard for them to find food when resuspended sediment turns the water cloudy, he says. And when the water is murky, sunlight can’t get through to aquatic plants.
Sediment also can contain nutrients like phosphorus, he adds, which feeds the algal blooms that are detrimental to lake life.
Effects of the dust-up can last longer than you’d think.
“Lake sediment includes organic matter, which is often slow to settle—taking days to return to normal,” Marr says.
Taking care of the lake
The good news? Marr says it’s possible to have fun in the water and protect our lakes.
University of Minnesota researchers prepare water samples.
His team recommends that all powerboats, when leisurely cruising or planing, should operate in at least 10 feet of water to minimize negative impacts on the lake environment. And during surfing, wakeboats should operate in depths of at least 20 feet.
“For all motorized boats, simply being careful about where you steer your boat and avoiding shallow spots can make a huge difference,” Marr says. “Staying in deep water when you’re out on the water—especially when wakeboarding or surfing—is an easy and effective way to enjoy and protect our waterways.”
Philanthropic funding has been “vital” to the team’s research, Marr says.
This study was supported by a University crowdfunding campaign with more than 200 donors from across the country, primarily from Minnesota and other Upper Midwest states. These gifts helped the team leverage additional funding from the Environmental Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources.
“We are finding that stakeholders are eager to learn the science of lakes and about understanding in a deeper way the results of our research,” Marr says. “Donations to our project help support our ongoing research as well as our time, travel, and other expenses associated with stakeholder engagement.”