Studies of Tug Lake
Tug Lake has been studied by state agencies, three universities, and a private consulting firm. The studies below are listed in the order they were done, so you can see how the understanding of the lake has grown. Where studies disagree, we say so. Figures labeled (measured) were taken directly from the lake. Figures labeled (modeled) or (estimated) were calculated from other data and are less certain.
Reports with a link can be read in full. Copies of the others are available by request to chair@tuglake.com.
Lake Survey Map, 1947
Who: Wisconsin Conservation Department, the agency that became the Wisconsin Department of Natural Resources (DNR)
When: February 1947
What they did: Mapped the lake's shape and depth.
What they found
Tug Lake covered 159 acres, with 2.8 miles of shoreline and a maximum depth of 21 feet (measured). Later studies still use this map's depth contours. The lake level was raised six to eight inches when the outlet dam was repaired in 2009, so the map may not match today's lake exactly.
Water Testing, 2016
Who: Chad Cason, Cason & Associates, for the Tug Lake homeowners
When: Sampled August 26, 2016
What they did: Tested water at six points after a severe blue-green algae bloom that summer.
What they found
Oxygen in the lake's deep water fell to nearly zero below 13 feet (measured), and phosphorus was high near the bottom. The inlet creek carried elevated nitrogen, phosphorus, and chloride. The report said more sampling was needed before any management steps could be recommended. Sampling took place after the bloom had passed, so its algae readings describe the lake on a good day, not during a bloom.
Citizen Monitoring Summary, 2017
Who: Dr. Todd Miller and a colleague, University of Wisconsin-Milwaukee, with Tug Lake Task Force volunteers
When: Mid-June to mid-October 2017
What they did: Volunteers sampled the deep hole weekly and sampled blooms wherever they appeared. A monitoring buoy recorded water temperature and algae levels.
What they found
Two kinds of blue-green algae, Microcystis and Dolichospermum, caused the blooms, and microcystin, a liver toxin, was the main toxin found. The lake mixed at least three times during the season, more often than most Wisconsin lakes. Because spring runoff did not explain the blooms, the report concluded that phosphorus was likely coming from the lake bottom or from groundwater, and recommended studying both.
Water Quality and Watershed Report, 2018
Who: Cason & Associates, for the Tug Lake Task Force
When: 2018
What they did: Studied the land draining into the lake and built a computer model of where the lake's phosphorus comes from.
What they found
The report concluded that the inlet creek is the main source of phosphorus and that more comes from the land than from the lake bottom (modeled). On that basis it judged aeration too costly for its benefit. It estimated septic systems at under 1 percent of the phosphorus coming from the land (modeled), and it found that farms along the inlet were doing an exemplary job of managing nutrients. It recommended shoreline buffers, no phosphorus lawn fertilizer, erosion control, and septic maintenance. The report is marked draft, and no final version has been located.
Internal Phosphorus Loading Study, 2018
Who: Dr. Todd Miller, University of Wisconsin-Milwaukee, with the Task Force volunteer sampling team
When: 2018 open-water season
What they did: Tested whether phosphorus released from the lake bottom drives the blooms, using oxygen and phosphorus readings at several depths and the monitoring buoy.
What they found
In July and August, the deep water loses its oxygen and the bottom releases phosphorus. When the lake later mixes, that phosphorus can rise to the surface, where algae use it. Whether a bloom follows depends on when the mixing happens and how warm the water is. In 2018 the mixing came after the water had cooled, which helps explain why that year's blooms were weaker and later. The report recommended toxin test strips for volunteers, staying out of the water during blooms, and further study of ways to control phosphorus from the lake bottom. Its estimates of how much phosphorus the bottom releases are approximate (modeled).
Sediment Assessment, 2020
Who: Cason & Associates, for the Tug Lake Task Force
When: Sediment cores taken February 6, 2020
What they did: Tested five cores of lake-bottom sediment for iron and phosphorus.
What they found
The sediment has a moderate ability to hold phosphorus (measured). The report recommended an aeration system to keep deep water above 2 milligrams per liter of oxygen, so the sediment would hold its phosphorus. This reversed the firm's 2018 view on aeration, and the report does not explain the change.
Alum Dosage and Application Study, 2022
Who: Bill James, University of Wisconsin-Stout
When: 2022
What they did: Tested six sediment cores from the deep basin and designed a possible alum treatment.
What they found
Phosphorus release from the sediment is moderate, and the amount of loose phosphorus in the sediment is modest compared with other lakes in the region (measured). The study outlined a treatment of alum applied in two doses, two years apart, to the lake bottom deeper than 10 feet, an area of about 64 acres (estimated). Because Tug Lake's water has very little natural buffering, the alum would need a buffering agent, which adds cost. The study gave no cost estimate and describes its design as a template to be adjusted.
Data Evaluation and Modeling, 2023
Who: Pat Oldenburg, Wisconsin Department of Natural Resources
When: June 6, 2023
What they did: Reviewed the lake's monitoring data from 2015 through 2023 to help develop a lake management plan.
What they found
There was no significant trend in summer phosphorus, algae, or water clarity from 2015 through 2023 (analyzed). Summer phosphorus averaged 33 micrograms per liter (measured). During much of summer 2023 the inlet creek flowed backward, so it delivered little phosphorus in bloom season (measured). Septic systems appear to be a very small share of the phosphorus load (modeled). The memo cautioned that treatments aimed at phosphorus from the lake bottom are usually used where phosphorus rises through the summer, which is the opposite of Tug Lake's pattern, so their effect here is uncertain. It also found that lowering summer phosphorus by about 10 percent could mean about half as many days of moderate algae blooms (modeled).
Toxin Summary, 2017 through 2022
Who: Dr. Todd Miller, University of Wisconsin-Milwaukee
When: Undated; summarizes the 2017, 2018, and 2022 seasons
What they did: Compared toxin results across the three seasons the lake had been tested.
What they found
Microcystin has been found in every season tested. Its levels vary widely from year to year and within a season, so the risk is occasional rather than constant, and a season's average describes it poorly. Two other toxins, cylindrospermopsin and nodularin, have never been found in the lake. The report recommended continued monitoring and tests to learn which nutrient most limits algae growth.
Water Quality Preliminary Report, 2024
Who: Ryan Haney, University of Wisconsin-Stevens Point
When: 2024 open-water season; report dated January 13, 2025
What they did: Sampled the inlet, the outlet, and the deep hole at two depths from June through September 2024.
What they found
Phosphorus near the surface at the deep hole averaged about 50 micrograms per liter (measured), above the state's phosphorus standard of 40 for this type of lake. Near the bottom, phosphorus rose through the summer and peaked in August before falling again (measured), a pattern that fits the release of phosphorus from the lake bottom. Nitrate was not found in any sample.
Water Quality Study, 2025
Who: Dr. Todd Miller, University of Wisconsin-Milwaukee
When: 2025 open-water season
What they did: Sampled the deep hole about every two weeks, sampled shoreline blooms, and ran the monitoring buoy, to support the new lake management plan.
What they found
About 78 acres of lake bottom have too little oxygen in late summer, varying from 50 to 92 acres between July and early September (modeled). Microcystin at the deep hole stayed low, peaking at 1.07 micrograms per liter. Shoreline bloom samples at a dock measured 531 and 698 micrograms per liter in late August and late September (measured), far above the swimming advisory level of 8. The report suggests nitrogen may also play a part in starting blooms, which would need further testing to confirm.
What the Studies Agree On, and What Is Still Open
- The deep water loses its oxygen every summer, and the lake bottom then releases phosphorus. Every study that measured it agrees.
- Microcystin is present every year, and shoreline blooms can carry far more toxin than the open water.
- How much phosphorus comes from the land and how much from the lake bottom is still unsettled. The 2018 watershed report pointed to the inlet creek. The Miller studies, the 2020 sediment report, the 2023 DNR memo, and the 2024 report all point to the lake bottom as an important source. The Lake Management Plan is weighing this question.
Page last updated: October 30, 2026.