By Danny Szydlowski, Graduate Fellow
January 22, 2025
My oars creak and mosquitoes hum as I row my boat out onto Peter Lake, surveying the results of our experiment. Brilliant streaks of teal water swirl behind the boat with each stroke of the oars. Even though I know why Peter Lake has a case of the blues, the water still looks out of place in the Upper Peninsula of Michigan. Usually, the lakes here come in shades of brown or are clear enough that you can see down 30 feet. Instead, I feel like I’m paddling in the Caribbean. It’s the summer of 2024, and we’re in the thick of our latest whole-lake experiment.
I make my way back to the dock and step out of the boat. From a standing position I can see nearby Paul Lake, which is nearly identical in shape and size to Peter. The two lakes are separated only by a thin strip of dirt and gravel, but today they couldn’t look more different. Peter is a sharp cerulean while Paul remains naturally clear with some brown staining. Their proximity and similar size make them an excellent place to do lake science (limnology). Since the 1980’s, the Cascade Project has been changing the conditions in Peter and comparing it to Paul, which is always left alone.
At the edge of the dock sits the plastic carboy we used to dye Peter Lake blue. It is still stained by Aquashade, a dye designed to block light from reaching algae. Unchecked algal growth can diminish recreational opportunities and negatively affect drinking water supplies because harmful blooms make the water look or smell unpleasant and may even secrete toxins into the water. But algae, like other plants, need light to grow, and the dye limits some of that growth. To be clear, we’re not recommending that lake users go out and dye their lakes blue. That would be impractical at a large scale and the long-term effects on the ecosystem are unknown.
Instead, in our small experimental lakes, we’re interested in the ecological response to changing light conditions and the resilience of the lake. That is, how difficult is it to cause an algal bloom? Being able to measure the resilience of lakes to algal blooms is the first step towards being able to manage them and make them more resilient in the face of global change. We followed the dye additions in Peter with fertilizer—again, don’t try this at home! Like light, nutrients are another important part of plant growth. We were surprised when, despite the dye, Peter changed from blue to green.
Back on the dock, I crouch over to dunk the carboy and give it one more rinse for good measure. As it fills with lake water, the residual dye takes on the hue of light blue Gatorade. I flip it upside down and dump the carboy into the lake like a winning team emptying the cooler on their coach. We think that Peter Lake bloomed despite the light-blocking dye because rain kept washing out the blue pigment. That’s the beauty of whole-lake experiments; because they happen with all the messy processes of a real ecosystem, there are always surprises. And surprises mean you always learn something.
Danny Szydlowski is a PhD candidate and CASC graduate fellow at the University of Wisconsin-Madison’s Center for Limnology, advised by Dr. Grace Wilkinson. His research focuses on lake resilience as well as their drivers of change, such as heatwaves and storms.