RESEARCH PAPER SUSTAINABLE AQUATIC RESEARCH www.saquares.com Sustainable Aquatic Research, 2(1): 251-273 DOI: 10.5281/zenodo.7881016 e-ISSN: 2822-4140 Assessment and classification of water quality using different water quality indices in the coastal waters of Eastern Aegean Sea L. Tolga Gonul 1* , Asli Kacar 2 , Filiz Kucuksezgin 1 , Idil Pazi 1 1* Marine Chemistry Program, Institute of Marine Sciences & Technology, Dokuz Eylul University, Izmir, Türkiye 2 Marine Living Resources Program, Institute of Marine Sciences & Technology, Dokuz Eylul University, Izmir, Türkiye Citation Gonul , L.T., Kacar, A., Kucuksezgin, F. and Pazi, I. (2023). Assessment and classification of water quality using different water quality indices in the coastal waters of Eastern Aegean Sea. Sustainable Aquatic Research, 2(1), 251-273. Article History Received: 14 February 2023 Received in revised form: 27 April 2023 Accepted: 29 April 2023 Available online: 30 April 2023 Corresponding Author L. Tolga Gonul E-mail: tolga.gonul@deu.edu.tr Tel: +90-5355894120 Keywords Seawater Quality Index Water Quality Variables Anthropogenic Activities E.I. Eastern Aegean Sea Introduction Various physical, chemical and biological processes mainly influence the coastal environment, as a complex system. Water quality affects both directly and indirectly the species abundance and diversity of marine living communities as well as recreational use of the coast. Excessive nutrient inputs, red tides and cyanobacteria (harmful algal bloom) are the main environmental problem affecting the coastal regions in the world (Anderson et al., 2002). Decrease in water quality is primarily owing to the increased levels of several contaminants such as heavy metals, petroleum hydrocarbons, pesticides and nutrients (Shahidul & Tanaka, 2004) giving Abstract The water quality monitoring in coastal areas of Aegean Sea interpreted through indices provides easy to understand and simple information for coastal managers and the general public. The Coastal Water Quality Index (CWQI) synthesizes the status of the eight water quality indicators such as chlorophyll a, total nitrogen, ammonium, nitrate+nitrite, total phosphorus, pH, dissolved oxygen; and fecal coliform into a single indicator of water quality. The CWQI compares measured variables to standard values. Seawater samples at 14 sampling points between 2014 and 2015 from Güllük Bay, Akköy and Ildır Bay of the Aegean Sea (eastern Mediterranean), have been analyzed seasonally in the current study. Investigation of environmental parameters demonstrated unsuitable water quality in some stations from Güllük Bay and Akköy. The anthropogenic inputs may be the likely reason for unsuitable water quality. However, generally good water quality was observed at Ildır stations indicating suitability of those areas for human activities like recreation. Furthermore, fecal contamination risk was detected at some stations in Akköy and Ildır.