Assessing the suitability of lakes and reservoirs for recreation using Landsat 8 Water Clarity

Water clarity has long been used as a visual indicator of the condition of water quality. The clarity of waters is generally valued for aesthetic and recreational purposes. Water clarity is often assessed using a Secchi disk, attached to a measured line and lowered to a depth where it can be no longer seen. We have applied an approach which uses atmospherically corrected Landsat 8 data to estimate water clarity in freshwater bodies by using the Quasi-Analytical Algorithm (QAA) and Contrast Theory to predict Secchi depths for more than 270 lakes and ponds across the continental US. We found that incorporating Landsat 8 spectral data into methodologies created to retrieve the inherent optical properties (IOP) of coastal waters was effective at predicting in-situ measures of the clarity of inland lakes. The predicted Secchi depths were used to evaluate the recreational suitability for swimming and recreation using an assessment framework developed from public perception of water clarity. Results showed approximately 90 percent of the waterbodies in our dataset were classified as “marginally suitable to suitable” with less than 10 percent classed as “eminently suitable” to “totally unsuitable – unsuitable”. The implications are that satellites engineered for terrestrial applications can be successfully used with traditional ocean color algorithms and methods to measure the water quality of freshwater environments. Further, operational land-based satellite sensors have the temporal repeat cycles, spectral resolution, wavebands, and signal-to-noise ratios to be repurposed to monitor water quality for public use and trophic status of complex inland waters.