I have archived the July 2024 water level chart (above, and at left). July was a hot and seemingly dry month, though in fact we received the average amount of precipitation for July of 3.53 inches. Most of the rain fell in the first half of the month and as a result, the lake level remained at or slightly above the top of the dam until the 17th when drier weather settled in for the rest of the month. We ended the month down -0.54 feet below the HWM, having lost only 0.37 feet of water, with evaporation accounting for about 3/4 of that loss. Still, even with only average rainfall for July, we’re at 140% of annual precipitation for this date, thanks to above average rainfall in March, April, and June.
Clear Water!
The real story for this summer, as anyone who’s been swimming knows, has been the amazing clarity of the lake water this summer. I posted a Midsummer Water Quality Update back on July 18th in which I marveled at the water clarity, and since then it has only gotten better! On Sunday the 28th, Kelsie French and I ventured out for our biweekly water quality monitoring session, both hoping that lake transparency hadn’t gotten any worse since our last visit. We were astounded when each of us recorded a secchi disk reading of 5.00 meters (16.40 feet). To give you an idea of how special this is, we’ve only recorded a transparency of 5 meters or better TWO other times going back to 1975: we had 5.3 meters in August 1994 and 5.27 meters in September 1990 (see the chart at left). You can see the blue dot representing the 5.00 meter reading all the way to the right on the 5 meter line. You can also see the previous 4 secchi disk readings going back to the 2nd of June, all of which were above 4 meters (13.12 feet) in depth. This degree of clarity in Clary Lake’s summertime water is pretty special. We can actually say it really doesn’t get any better than this.
It’s All About Nutrients
I’ve been saying all along that the high flushing rate we’re seeing this year is the main cause of our good water quality this summer (chart at left). However, high outflow rates imply high inflow rates and that is often not conducive to clean water due to pollution of the runoff with sediment, but as usual, there’s more going on here than meets the eye. Last year our outflows were quite high, very nearly the same as this year and yet last year’s water quality, though reasonably good, wasn’t nearly as good as it is this year. What’s going on?
It’s all about nutrients. As of the end of this July, 11,714 acre feet of water (or 1.62 full lake volumes) has passed over or through the dam since the beginning of the year taking with it nutrients that feed algae. Yes that’s a lot of water, but we need to look at not just the volume of water leaving the lake but the source of the water that is replacing what’s been lost: some of it clearly is runoff from precipitation but some of it, sometimes a lot of it, is ground water. In 2023 we received over 60 inches of precipitation and ended the year with a very high ground water table. A lot of that ground water has been seeping into the lake this year to help replace some of the water that has been lost downstream. This ground water is much cleaner than surface runoff water as it contains no sediment or Phosphorus to speak of. All this “clean” water entering the lake nicely explains the clean, clear water we’re seeing this summer as well as the exceptionally low Total Phosphorus result we saw back in June (0.011 mg/L). In short, this summer’s clean water is largely due to last year’s excess precipitation.
The high outflows last year, similar in volume to this year’s, were primarily due to excess rainfall, meaning there was a lot of surface runoff polluted with sediment entering Clary Lake in 2023. This was not conducive to the clearest water! The picture at left shows a washout on Route 126 as the result of 5.5 inches of rain we received on May 1st. One month after this picture was taken we had a short but intense algae bloom (picture below) as result of the tons of sediment that washed into Clary Lake during that rain event. It’s rare when we can correlate an algae bloom with the actual rain/runoff event that effectively caused it. This bloom burned itself out quickly and thanks to the high flushing rate last year, we avoided continued blooming during the summer.
We have a pretty good idea of how much water is flowing into the lake by comparing how much the lake should fall based on current outflows with how much the lake actually falls. For example, if enough water is leaving the lake to cause the lake level to drop 1 inch in 24 hours but it actually only drops 1/2 an inch in that time, then we know that enough water is flowing INTO the lake to replace some of what’s lost so as to raise the level 1/2 an inch. That water flowing into the lake can come from two sources: from surface runoff or ground water seepage. Usually it is some combination of the two. A quick look at how much precipitation we’ve received recently can indicate which source, surface water or ground water, is mostly at play.
Hopefully our exceptional water quality will continue through August and into the fall though I do anticipate a drop in transparency and increased algae counts in September when Fall turnover mixes the lake water. It remains to be seen whether we’ll see an algal bloom this fall. Time will tell.