Lake Minnetonka's western bays were frozen solid. Just off the shore in Cooks Bay, garbage trucks could safely drive right above the icy water.
This isn't the logical time to study a lake. But for a team led by University of Minnesota-Duluth researchers, that was the point: They want to know how shortening winters — and less ice cover on lakes — may increase the presence of harmful algae blooms and impact the fishery.
Aside from people who ice fish, the general assumption is that not much happens in lakes during winter, said Andy Bramburger, a research associate from the U's Duluth campus.
But he thinks winter, especially late winter, may be more impactful on lakes' cycles than scientists previously understood.
"With climate change, our winters are getting shorter and shorter and we're losing winter and we really don't know what the impact of that is," Bramburger said. "We don't know how important that might be."
To find out, Bramburger and researchers from the University of Minnesota, the U.S. Geological Survey and the University of Maryland gathered data last week from a half-dozen lakes across Minnesota.
Shorter winters likely affect everything you'd do involving a Minnesota lake
The biggest effect of climate change on lakes isn't necessarily how warm it gets, but how cold it doesn't get.
These warmer winters are shorter, so more sunlight can reach the water earlier, jumpstarting algae production and affecting the lake's biology.
"That translates directly to summer fish production," Bramburger said. "How many walleye people can catch on these lakes can be determined by what's going on under the ice in the winter."
While shorter winters sparking earlier algae production could mean more nutrients cycling up the food chain to sport fish, it could also mean more of the toxic blue-green algae that has grown in prevalence across Minnesota.
These harmful algae blooms, which are technically made up of cyanobacteria, have been blamed for sickening humans and killing animals — including pet dogs — that drink contaminated water.
For many Minnesotans, this could be a big deal.
"If you have a cottage and you like to swim or waterski, or further north where people actually take a lot of drinking water for their cottages right out of the lakes, having toxic algae blooms is potentially a big concern," Bramburger said.
Data from space could help draw broader conclusions
The other part of this research involves checking the accuracy of satellite data on ice thickness and snow cover.
Scientists have used satellite data to study oceans and the Great Lakes, but using it for inland lake research is new, Bramburger said.
If this team proves that satellites can accurately measure ice and snow on lakes — and they find a connection to algae — they might be able to make some broad conclusions on climate change's effects on lakes.
They're making sure to study each kind of Minnesota lake: green, brown and blue lakes.
Each has a different makeup, so more light toward winter's end may affect each type differently, said Ted Ozersky, a Duluth researcher studying lake biology.
• Green: A lot of nutrients and algae, so they're considered "productive" lakes.
• Brown: Lots of decayed organic materials and little light.
• Blue: Clear water and lots of light, but not a lot of nutrients.
"If we can tell something useful, then we can use sat data to survey thousands of lakes rather than visiting each one, and then extrapolate some of our findings," Ozersky said.
At this point in the research, there are so many unknowns regarding what goes on beneath the lake ice, Bramburger said. And it's important to figure them out soon.
"We need to kind of race against time a little bit to find out how important winter is and how active things are down there before we've really lost winter."