A total of five volunteers collected measurements and samples on Clear Lake in 2013 and/or 2014. A
total of six sites across the lake were visited up to seven times between May and October each year. A
typical sampling event consists of one or more volunteers recording environmental conditions (water
temperature, air temperature, cloud coverage, wind speed/direction, precipitation, water appearance,
water color, water odor), the presence of invasive species, measuring the water clarity, and collecting a
bacteria sample.
Between 2013 and 2014, Dakota Water Watch began switching to a new system of Lake IDs. Please use
this guide to compare sites between the two years. I apologize for any confusion.
4807AAA = 4807-01
4807DDD = 4807-02
New site = 4807-03
4807QQQ = discontinued
4807TTT = 4807-04
4807BB = 4807BB
Water Clarity
Water Clarity measurements ranged from 0.56 meters to greater than 1.23 meters in 2013. In 2014, no
measurement was ever less than 1 meter. Although the largest measured Secchi depth was 2.00
meters, several readings collected along the shoreline were greater than the available equipment could
measure and could have been over 2.00 meters. All of these transparency measurements are above
average when compared to other lakes in Eastern South Dakota.
The Environmental Protection Agency has calculated a desired Secchi depth value for lakes within each
of the country’s 14 distinct ecoregions. The value for ecoregion 6 (the ecoregion containing Clear Lake)
is ≥1.36 meters. This value is only a general guideline, but it can give an idea as to the transparency
value that lakes within the ecoregion should have.
Bacteria
Dakota Water Watch uses E. coli bacteria an indicator organism. If E. coli is present in a water sample, it
is a good indication that the water has been recently contaminated by fecal material. It is impossible to
determine the exact cause of any pollution using our methods, but likely sources include livestock,
wildlife, and/or malfunctioning septic systems. South Dakota uses an immersion recreation standard of
≤235 colony forming units (cfu)/100mL of sample water.
Over the past two years, E. coli samples ranged from no detection to as high as 286 cfu/100mL. There
were no exceedances of the immersion recreation standard in 2013, but there were two in 2014, both
occurring at site 4807-04. One exceedance also occurred in 2012, but at a different location (4807-02).
Like in 2012, follow up sampling was done after each of the high bacteria results. These samples
showed that the bacteria numbers quickly fell below the ≤235 cfu/100mL standard. While it is possible
to have instances of high E. coli values, I still do not believe that bacteria are a persistent issue on Clear
Lake.
