Based on the mean values of seawater environmental elements and the Seawater quality standard of China (GB 3097-1997, 1998), the values of each seawater environmental element should be normalized and divided into corresponding pollution level. The maximum normalized values of each seawater environmental element are chosen as the representative value of each site. Seawater Environmental Quality Index is calculated as the highest index among the pollution indices of the seawater environmental elements.
The formula can be given by: