“I remember being on this lake seven or eight years ago and just cutting a path through the algae,” Jerry Spetzman remarks as we motor across South Lindstrom Lake. Today, the water is so clear that we’re able to lower a Secchi disc 12-feet deep into the water before it vanishes from sight. “At the end of that road, there is a sand-iron filter that removes phosphorus from runoff before it goes into the lake,” he continues, “and the city park over there has a below-ground filtration practice as well.”
Spetzman is the administrator of the Chisago Lake Improvement District (LID), a special-purpose local unit of government that oversees flood prevention and water-quality improvement efforts for 19 lakes and 7000 acres of surface water in Chisago County. The LID was formed in 1976 to address high water and the flooding of shoreland homes, and now maintains a system of channels and weirs designed to keep lake levels low. For Spetzman, however, the best part of his job is getting out on the lakes once a month to monitor water quality.
As we move from lake to lake, Spetzman demonstrates how to collect water samples and the various measurements used to evaluate lake water quality. Three variables – water clarity, total phosphorus, and chlorophyll – are combined to create a metric known as a trophic state index. Lakes with a low trophic state index have exceptionally clear water and are considered “oligotrophic.” These lakes are most common in cold regions with little to no development, like the Boundary Waters, and they usually have rock bottoms with little muck or sediment.
In contrast, “eutrophic” and “hyper-eutrophic” lakes have excessive amounts of nutrients, especially nitrogen and phosphorus, and are dominated by algae and aquatic plants. In the middle, mesotrophic lakes are characterized by relatively clear water with enough nutrients to support a healthy food web and abundant fish.
To measure chlorophyll, scientists collect water samples from a few feet below the lake surface and strain it through a filter to collect algae that is suspended in the water. These samples are then sent to a lab for analysis. A few years back, Spetzman began noticing that the color of the algae samples on a white filter corresponded almost perfectly with the lakes’ overall water quality. “We started filtering the algae and noticing different colors and I wondered if that means anything,” he says. So, he picked up a few Martha Stewart color charts and began bringing them along on the boat. “Now I’ve been doing it long enough that I can pretty consistently estimate the water quality tropic index on a lake purely based on the color,” he laughs. Samples collected from higher quality lakes will be in the “yellows and creams,” while samples from lower quality lakes will be greener.
During today’s water monitoring trip, Lindstrom Lake and the north basin of Chisago Lake both have clear water with Secchi disk readings of 12-14 feet deep. According to Martha Stewart, the algae samples from both are the color of a chopstick. In the south basin of Chisago Lake, the water clarity is only 8 feet deep and the algae looks more like parchment paper. We find the clearest water in the channel between North Center and Lindstrom Lakes where there are loads of aquatic plants amidst crystal clear water. Here the algae sample is the color of heavy cream.
Thanks to runoff-reduction projects in the surrounding communities, water quality is improving in 100% of the lakes for which the Chisago LID has monitoring data. In fact, North and South Center Lakes improved enough to be removed from Minnesota’s impaired waters over the winter. “They still aren’t pristine,” Spetzman explains, “but they crossed the threshold from impaired to non-impaired. Basically, they improved from a D grade to a C.”
As water quality has improved, Chisago County lakes are again living up to their Ojibwe name “Ki Chi Saga,” which means fair and lovely waters. For Spetzman, that means less days boating though green masses of algae, and more days collecting clear water samples with algae in shades of chopstick and cream.