Secchi transparency at Rocky Fork Lake ranged from 63 to 147 inches during the first 10 days of monitoring, representing a difference of 7 feet. Because algal biomass and suspended soil materials are generally the driving forces in determining water clarity in Missouri’s lakes, we can look to these parameters to help explain the changes we see in Secchi transparency.

The first big shift was an increase in clarity on May 15 th (Figure 3). This 39% increase in Secchi can probably be attributed to the decrease in algal chlorophyll and remarkably low NVSS levels (Figure 3). This peak in clarity didn’t last long, as there was a decline to 100 inches of clarity the next day when algal chlorophyll increased slightly. We see that the minor changes in chlorophyll and NVSS from one day to the next are reflected in differences in clarity, and that both parameters play a role in determining the clarity. When chlorophyll increased to over 10 ug/L on May 20th the clarity responded by dropping below 70 inches (Figure 3).

Be aware that in lakes with high algal biomass (chlorophyll > 20 ug/L) the changes in transparency are minimal even when chlorophyll shifts dramatically. During the algal bloom and subsequent die-off in Little Dixie Lake, the Secchi transparency only fluctuated by 16 inches (ranging from 13 to 29 inches).