In Sri Lanka, the "biggest maritime disaster"occurred on May, 2021. The ship carried 1486 containers of chemicals, including low and high-density polyethene, methanol, sodium methoxide, nitric acid, urea, and lubricant oil. This multi-faceted and complicated disaster involves numerous environmental issues that could have significant consequences. The present study aimed to evaluate chemical contamination in coastal waters from Negambo to Bentota by analyzing water samples, biological samples, phytoplankton, biotoxins, and heavy metals. The research findings revealed that the average nitrate concentration in the study area's coastal waters ranged from 0-0.19 mg/L. The highest nitrate and phosphate concentrations were recorded near the MV X-Press Pearl ship. The chlorophyll-a concentrations in the coastal belt ranged from 1.8 + 0.6 to 11.8 + 1.1 mg/L, and the highest was near the MV X-Press Pearl ship disaster in X2. The most abundant phytoplankton recorded were harmful diatoms; (Nitzcha sp., Amphora sp., Chaetoceros sp. and dinoflagellates; (Gymnodinium sp., Ceratium furca, Prorocentrum sp., Peridinium sp., Dinophysis caudata in the sampling location near the ship and where the highest Saxitoxin concentration was detected (0.230.06 g L-1). It might be due to the release of the high concentration of phosphate and nitrogen, which directly affect the growth of algae, diatom, and dinoflagellates following increasing of chlorophyll-a content. The location, which was extremely close to the MV X-Press Pearl ship, sank and had the highest oil and grease content. Lead (Pb), Zinc (Zn), Copper (Cu), Chromium (Cr), Cadmium (Cd) and Nickel (Ni) were the most common heavy metal pollutants in the study area's coastal waters. Thus, the results of the present study revealed that the ship disaster had a significant impact on coastal environment water quality which may affect ocean biodiversity, the ocean's health, fishery resources and the economy of the fishing community and seafood industry.(c) 2022 Elsevier B.V. All rights reserved.