Clary’s water quality this summer is in a word, awesome. I’m sure  any of you who’ve been swimming will agree! The clarity so far this summer is measurably better than we’ve seen in a long time. Last weekend on July 14th Kelsie French and I went out for our biweekly water quality monitoring session at the “deep hole” and we both had secchi disk readings of 4.81 meters (15.77 feet). This is the deepest secchi disk reading we’ve recorded since a 4.88 meter (16.00 feet) reading back in May 2003 (see chart at left). There have been less than 10 secchi disk readings as good or better than today’s, going back to 1975, and none in the last 20 years. Extraordinary. Today’s secchi disk reading was actually the 5th consecutive reading deeper than 4 meters, also extraordinary. We haven’t had a stretch of clear summer water like this in Clary Lake for a long time.

The latest Dissolved Oxygen (DO) profile (see featured image above) shows the lake has a well established thermocline between 3 and 4 meters. DO at 4m was 3.2 mg/L and the temperature was 22.4°C; DO at 5m was 0.1 mg/L and the temperature was 19.1°C. Once again, there’s essentially no oxygen below 4 meters. The lack of oxygen in the bottom 1/3 of the lake is concerning because it leads to internal loading of Phosphorus. However, that won’t really impact water quality until this fall when the bottom Phosphorus rich water mixes with the upper surface water where algae live and sunlight can reach.

Also somewhat concerning is the water temperature (chart at left): the top 3 meters of the lake are all at or above 28°C (82.4°F). The highest surface water temperature we’ve ever recorded was just one degree centigrade higher, 29°C (84.2°F) in early August, 2019. We’re already almost there now and there’s still some hot weather ahead. Warm water favors algae growth. Fortunately, Total Phosphorus is low: back on June 16th our first Total Phosphorus core water sample tested 0nly 0.012 mg/L (milligrams per liter). This is a fantastic result, it is the lowest value we’ve recorded since obtaining a TP of 0.011 mg/L in August 1993. We’ve only seen 0.012 mg/L one other time, in August 1972. Only 6 TP tests were recorded between 8/01/1976 and 8/01/1993. You can see the values of all the Total Phosphorus tests back to the start in the chart at left.

I attribute this summer’s great water quality to a high flushing rate, higher than in any of the 5 previous years. As of today, we’ve already exchanged the full volume of Clary Lake 1.62 times. High outflows result from high inflows (obviously?) and we’re just fortunate that all the rainfall this year has not introduced significant sediment which carries with it nutrients, including Phosphorus.