The ocean is the most significant contributor to oxygen production on Earth due to the presence of chlorophyll-a contained in phytoplankton. One way to determine the concentration of chlorophyll-a is by using a smartphone camera through the HydroColor application. The data obtained through the HydroColor application does not directly provide chlorophyll-a data, instead, it provides red, green, and blue (RGB) wavelength data. This RGB wavelength data is then input into an equation to generate the chlorophyll-a concentration. This study aimed to evaluate the HydroColor application to estimate chlorophyll-a concentration. The research was conducted in Banten Bay, using field data collected with a smartphone and compared against laboratory test results and MODIS satellite imagery. Among several regression models tested, the logarithmic model showed the best correlation with laboratory results, with an R² value of 0.83 and a correlation coefficient of 0.876. The HydroColor application can be practical in coastal water bodies with a smartphone featuring a high-resolution camera. This study demonstrates that HydroColor has the potential to serve as an alternative method for estimating chlorophyll-a concentration in Banten Bay.
