Final Lake Testing Report - 2020

The final testing of Finger Lake water quality for 2020 was done on August 26, 2020. Typically, testing of lake quality parameters is done four times per year - two weeks after ice out and some point the last two weeks of June, July, and August. This year because of COVID 19 the state testing labs were not available in March/April so the WDNR canceled the two weeks after ice out sampling but instructed us to precede with the remaining testing periods. We also typically assess the lake for invasive species in July but because of COVID 19 we canceled the 2020 assessment. We felt comfortable doing so because of the extensive invasive species testing in 2019 and the very positive results showing no invasives except the Chinese Mystery Snail - which poses no hazards. Invasive species assessments will hopefully resume next year. Before sharing the results of this years testing, I would like to thank the people who give up their time to conduct this important work on behalf of the FOFL Association. Please join me in thanking these folks when you have a chance:

Lake Water Quality Testing - Bill Abba and Sue Sazama

Invasive Species Monitoring Team - Bill Abba. Sue Sazama, Laurie Skotzke, Melanie Howe, and Bret Ewer

Here are the key observations from the lake water quality testing for 2020:

1) Water levels remained very high all year, which is not typical. Usually water levels drop over the summer months, and they actually did drop four to six inches in mid-summer this year, but rose again in July/August to levels experienced last spring. Water continues to flow into the outflow canal along Rangeline Road and water levels in the canal remain at extraordinarily high levels too.

2) Water clarity increased as measured by secchi disk from eight to ten feet in 2019 to twelve to thirteen feet in 2020. The color of the water remains brown stained from the natural tannic acid from pine trees added to the lake through runoff from the surrounding watershed. The brown color  was less intense this year likely leading to the increased light penetration and the deeper secchi disk readings. The presence of tannins in lakes in northern Wisconsin is widespread and completely natural. The increase in runoff the past few years because of higher rainfall and snow levels is the cause of the increase in tannins.

3) The increased light penetration noted above has resulted in improved dissolved oxygen ( D.O. ) levels deeper in the lake. Finger Lake routinely has very good D.O. levels capable of supporting all forms of life. While D.O. levels in the past were very good right to the bottom in 30 feet of water, recent years has seen the amount of D.O. fall off to near zero below twelve to fifteen feet of water to the bottom. This was likely the result of the reduced light penetration and the inability of oxygen producing plants to survive in deeper water. This year, good oxygen levels were found down to twenty feet and then they dropped to zero the rest of the way to the bottom. There was no oxygen in water deeper than twenty feet which was an improvement from last year's depth of twelve to fifteen feet. As observed last year, it is expected that when fall turnover occurs in late September or early October, oxygen levels will recover all the way to the bottom and should remain at a higher level much of the winter. This cycle will repeat each year. 

4) The improved light penetration may be having a less desirable affect too. While in the past couple of years we have not seen the massive blooms of Southern Naiad  observed a few years back, this nuisance weed did increase this year. The improving light penetration is likely allowing this plant to grow to a greater degree this year. Southern Naiad grows from the bottom of the lake up to the surface so light penetrating deeper in the lake can only help this plant grow. The highly brown stained water of a few years ago probably inhibited it's growth. While little surface growth was observed this year, widespread growth on the bottom in shallower water was seen. Continuing increases in water clarity could lead to the undesirable extensive growth previously observed. 

5) Testing results for chlorophyll and phosphorus have been received for the June and July testing and the levels of these two important measures is consistent with recent years. The chlorophyll level tells us how much microscopic algae is growing in the lake. Phosphorus is a critical plant nutrient and when the level is high, excessive plant growth can result. Both of the tests were at reasonable and historical levels so there are no issues there.

In summary, the water quality of Finger Lake remains very good. The lake is healthy and while some natural changes, i.e. tannin levels, are occurring, they pose no long term issues for the lake. Oxygen levels in the summer months in deeper water continues to be something to watch, but this situation is occurring in a number of deep lakes up north. The biggest item to watch is as water levels return to more normal levels and the water continues to clear and become less brown, will we see a return of the massive growth of Southern Naiad. This is something to keep an eye on.