The Citizen Lake Monitoring Network (CLMN) is a volunteer force of more than 1000 individuals that collect and report data to the DNR on the million acres of Wisconsin that is covered by water. For Pike Lake, that data collected includes water clarity with the use of a Secchi dish, a circular disc roughly 9 inches in diameter and divided into alternating black and white quartiles. Dropped into the lake on a cord, the data collected is the depth at which it disappears from sight by the naked eye when looking down into the water from just above the surface. This “technology” was first used in 1865.
Best measured in the sunlight at a of time of day when the sun is overhead and collected bimonthly. It is measured over the “deep hole” on the East side of the lake. Simultaneous to this measurement, dissolved oxygen is also measured, but at 5 different locations around the lake and at varying depths. All data collected is recorded on the CLMN website.
Lake water clarity is dependent on a variety of factors. The most common is suspended sediment from runoff, inlet waters, erosion of cropland and in shallow lakes, wind, boat propellers and even large fish stirring up the bottom. Algae and other by-products of living material can contribute to both turbidity and lake water color. Obviously heavy lake use or heavy rains and/or winds can impact lake clarity. On Pike Lake the depths of clarity can vary from barely 4 feet to over 7 feet in the same location.
Some examples of past data include 2019 recorded values that were relatively poor by historical standards, ranging from less than 5 feet to barely exceeding 5 feet. Recall it was a rainy season and the water level was historically high. This suggests above normal levels of runoff and/or inlet volumes.
In 2018, the depths recorded were more typical. With high water levels in the Spring (4.75’), to July and August values straddling 7’ with normal water levels and then late in the summer with lower water levels and likely algae blooms, it dropped back to 4.5’. In recent years, the ranges have consistently been greater than 4 feet at worst and exceeding 7 feet but less than 8 feet at best.
For 2020, the earliest measurements were in late May and was a surprising 87 in (7’ 3”) when the water was still high. In mid-June the reading was a typical 67 in (5’7”) after some significant rain. On July 1, with remarkably clear water the reading was 80 in (6’8”).
The contribution of algae to suspended sediment is a complicated issue, dependent on variable lake depths, penetration of sunlight and available nutrients in the lake, especially nutrient rich plant material lying on the bottom of the lake. We must be constantly vigilant about all of the contributors to decreased lake clarity. Hence the many lake volunteers around the state, hope to contribute to the data base that may eventually reveal successful strategies to keep our lakes clean and vital.
Dissolved oxygen is also measured on Pike Lake at 5 separate locales. Aside from the “deep hole” where it can be sampled at 5 foot intervals, allowing multiple readings, the other locations are typically 5’ or less and only one or two values are recorded. Commonly the highest readings are in shallow water above the lake floor, where lake vegetation is….fish habitat. These readings are nearly always higher than at any depth in the “deep hole”. Deep holes are stratified (layered) and the water temperature and the dissolved oxygen values can vary profoundly from one depth to another, moving the probe less than 5 feet. It is left to the limnologists to interpret these data, so they are submitted to the DNR after each data collection.