ABSTRACT This research was conducted in March 2020 at Mesjid River Estuary of Dumai City, Riau Province. The aim of this research was to determine the pollution levels in the Mesjid River Estuary based on organic matter parameters and E. coli bacteria. DO analysis refers to SNI 06.6989.14-2004, BOD5 refers to SNI 06- 2503-2009, BOT refers to SNI 06-6989.22-2004 and E. coli bacteria refers …