Bleaching is a major threat to coral reef ecosystems around the world. This study aimed to determine the effect of turbidity on the severity of coral bleaching and mortality in Kalimantan due to thermal stress and high solar irradiation caused by the 2015 El Niño. Coral colonies in eighteen permanent bleaching belt transects (50 m x 1 m) in six sites were observed from June to November 2015, coinciding with the 2015 El Niño. Water depth, sea surface temperature (SST), salinity, turbidity, sedimentation and total suspended solid (TSS) were measured on the same transect. Three permanent bleaching belt transects were applied randomly on each reef. Species and bleaching status of each coral colony (diameter > 5 cm) in belt transects were identified. The bleaching status was measured Coral species were identified in the field. Results showed that the 2015 El Niño was a major disaster for reefs on the southeast coast of the Kalimantan. Of total colonies (N = 12,954), 45.4% of colonies were bleached and 14.7% of colonies were died during the period of July to November 2015. Turbidity, TSS, and sedimentation were negatively correlated with the bleaching mortality index (BMI). Coral bleaching in clear and deep waters occurred earlier and increased rapidly compared to that in turbid waters. However, the severity of coral bleaching in turbid zone increased dramatically when the turbidity dropped to <3 NTU. Turbidity >5 NTU could provide shade, in which the proportion of dead corals was only 3.5%. The severity of coral bleaching in turbid zone is not solely due to thermal stress and solar irradiation; it may also be influenced by a history of exposure to high turbidity and low salinity. Keyword: El Niño 2015, coral protection, coral bleaching, turbidity, shading