2021 State of the Lake Report

As we have reported in the past, each year FOFL conducts lake water testing to keep tabs on the current state of Finger Lake water quality and to identify and monitor any trends that may be developing. This past year proved difficult to keep important lake management projects going because of COVID, but an abbreviated lake water testing program was completed. Early testing in April was canceled because the State lab we use to conduct some tests was converted to a COVID testing operation. Testing got back on track after April and we were able to complete all three remaining test dates.

Sampling and testing were carried out by Sue Sazama and Bill Abba at one site on the lake, the deepest place at 30+ feet. Testing is typically done four times per year; two weeks after ice out, and the last two weeks of June, July, and August. The results are reviewed by DNR lake scientists at the end of the year and we receive a report with their thoughts. I will summarize the findings below:

• Water levels remain significantly and atypically high; water continues to discharge into the outflow pond and water levels in the pond also remain atypically high.

• Water clarity increased significantly with secchi disk readings doubling from 6 feet to 12 feet. Lake water was significantly less brown in color this year and this contributed to the increasing water clarity numbers. The level of tannins in the lake appears to have decreased significantly, thereby reducing the brown color, which in turn allowed light to penetrate much deeper into the lake. Tannins are natural chemicals produced by plants on land that drains into lakes. For some unknown reason the amount of tannins in Finger Lake declined which would not have been expected with the continuing high water levels.

• The amount of chlorophyll and phosphorus in the lake remains at typical levels for Finger Lake and below the average for northern lakes. Phosphorus is a vital plant nutrient and at high levels can lead to algae blooms in lakes. The phosphorus level in Finger Lake is low enough that algae blooms are unlikely. The lower chlorophyll levels in the lake indicates limited growth of algae caused by the lower nutrient levels in the lake. This would be expected in lakes like Finger Lake.

• Dissolved oxygen (DO) levels in the lake are quite high which is very positive. The high levels of DO will support a high quality fishery and fish kills are not likely. As we have observed the past 2-3 years, DO levels drop off rapidly and approach zero in water deeper than 15 feet. I suspect this is a summer situation and once fall turnover occurs in September, DO levels are good at all depths throughout the lake through the winter and until spring turnover occurs in April. Very low DO levels found in water deeper than 15 feet likely occurs, therefore, from late April through early September only. During this time, fish and aquatic animals must move to water less than 15 feet deep.

• Finger Lake had a thermocline during the summer months which occurred at about 15 feet. Below that depth water temperature decline significantly and rapidly as does DO. This situation is typical in deeper lakes where light cannot penetrate into deeper water allowing plant life to grow and produce oxygen. This likely occurred in recent years on Finger Lake because the brown color reduced light penetration and limited plant growth, especially in deeper water. The formation of thermoclines is common in deeper northern lakes and is not a concern.

So what does this all mean and where are we likely headed. First, Finger Lake remains a very good water quality lake that is healthy by all measures we test. No concerning water quality issues exist at this point. Second, in recent years, Finger Lake has experienced changes that have resulted in some test numbers moving around, and these changes are likely to continue. The most significant factor causing these changes is the high water level and high levels of tannins in the lake that come from runoff from the surrounding watershed. High snowfall and rainfall amounts over these years brought much runoff into the lake and much higher tannin runoff than we typically would see. It is difficult to know how weather patterns will change moving forward, but at some point, we can expect the weather cycle to change. Just remember, it was not that long ago that we had a multi-year drought that dropped the lake level as much as four feet. The fluctuations created by these changes in the lake are not concerning and are part of the natural cycles.

One thing does concern me, however, and warrants watching. As the lake level drops to more typical levels and the amount of tannin in the lake declines, water clarity numbers will continue to increase, and light will penetrate deeper into the lake. For those of us who were around when we dealt with the huge surge in the plant Southern Naiad a few years back, I am sure you recall the issues it created. I believe that the reduced light penetration experienced because of high water levels and tannin runoff the past few years is why we have seen a major decline in the amount of this nuisance plant in the lake – it needs more light than is available in the current lake condition. I am watching to see if we may be on the verge of another Southern Naiad bloom as things return to a more normal place. Only time will tell.

If you have questions, give me a call at 920-667-4953.

Bill Abba