October 20, 2019 — Beaver Lake Secchi Day Data Released for 14th Year

On Aug. 17 for the 14th year in a row, volunteer citizen scientists collected water quality data on Beaver Lake in Northwest Arkansas during the annual Secchi Day on Beaver Lake event. Beaver Water District (BWD) staff then analyze data and produce a report that helps answer this question: How is the water quality in Beaver Lake?

Matthew Rich, Environmental Specialist with BWD, spoke about results and data from Secchi Day with the BWD’s Board of Directors at their monthly meeting held on Oct. 17.

This year, 37 teams collected data and water samples from 35 duplicated sample sites throughout the lake. Sampling teams take Secchi disk readings to determine water clarity. They also collect water samples that are then tested by BWD lab staff for chlorophyll-a, total phosphorus, and total nitrogen to determine algal density and nutrient concentration. Secchi depth is a measure of water transparency that involves lowering a black and white disk into the water and recording the maximum depth in which the black and white pattern can be distinguished from above the water’s surface.

“Secchi depth is inversely related to the concentration of chlorophyll-a. Therefore, as chlorophyll-a decreases, Secchi depth increases.” Rich said. “When it comes to producing drinking water, greater Secchi depths and lesser chlorophyll-a and nutrient concentrations are best,” he added. “While Secchi Day is only one day out of the year, the data collected provides a better picture of the interannual variability in water quality at the different sites that are sampled every August.”

This year’s data shows that most water quality parameters deviated away from previous 13-year averages.  The whole-lake average Secchi depth this year was around 8.2 feet, which is a slight decrease in clarity from the long-term average of 8.9 feet.  The whole-lake average chlorophyll-a this year was 9.01 parts per billion (ppb) which was significantly greater than the long-term average of 7.49 ppb.  The higher-than-average chlorophyll-a concentration, and lower-than-average Secchi depths, this year were driven in part by unusually high rainfall totals in the watershed in the weeks and months leading up to Secchi Day. These late season rains delivered increased sediments and nutrients into Beaver Lake. However, both Secchi depth and chlorophyll-a averages were well within the normal variations for the 13-year dataset.

“Year after year, Secchi Day continues to provide BWD with excellent data concerning the water quality in Beaver Lake.  There has been quite a bit of variability in the last thirteen years, but the silver lining is that at this point, according to Secchi Day data, we do not have any indication that water quality is degrading,” Rich said.

James McCarty, BWD’s Manager of Environmental Quality, added that “Secchi Day is only one example of our ongoing efforts to monitor and maintain the water quality of the lake. We look at this data and much more to help us keep watch on key indicators of water quality problems and assess our restoration and protection efforts within the watershed.”

To read this year’s Secchi report, go to the Secchi Day page on the BWD website at https://www.bwdh2o.org/education-outreach/secchi-day/ and the report will be on the bottom left. Mark your calendar now. The 15th Annual Secchi Day & Science Festival on Beaver Lake will be held Aug. 15, 2020. The event includes many partners such as the U.S. Army Corps of Engineers-Beaver Lake, the U.S. Geological Survey, the University of Arkansas Cooperative Extension Service, Northwest Arkansas Stormwater, Hobbs State Park, Northwest Arkansas Master Naturalists, Beaver Watershed Alliance, Beaver Lake Fire Department, Ozarks Water Watch, OneCommunity, The Ozark Society, 3W Magazine, KNWA, North American Lake Management Society, and Girl Scouts Diamonds of Arkansas, Oklahoma and Texas. Secchi Day is one of the premiere water public awareness and education events in Arkansas.