Water quality indexes are a tool used to evaluate the physicochemical characteristics of a water body according to its use. The present study proposes the inclusion of oil and grease (OG) as a new water quality index (ICAMPFF-GA) parameter for the preservation of marine biota in tropical areas, since it is a typical pollutant found and measured in water bodies, causing damage to the aquatic environment. The normalized curve for OG was defined based on the percentage of surviving microorganism under a lethal concentration exposure of OG. The ICAMPFF-GA suitability was evaluated by its application to analyze marine water quality in the area of the sea outfall in the city of Cartagena, Colombia and comparing the trends of the outfall flow and the rainfall for 2017. Physical chemical data analyzed for the year 2017 shows that OG varies from 0.0 to 3.8 mg/L. The results show that the water quality index increases when rainfall and flow values increase for the rainy season. The ICAMPFF-GA can be a tool to evaluate the water quality of marine waters affected by the discharge of waters with oil and grease.