To get as accurate a picture as possible of the current water quality of a beach, the EPD calculates the geometric mean E. coli levels of the five most recent samples it has taken. Most gazetted beaches are sampled at least weekly, so a typical beach grading figure represents the state of a beach’s water over the previous month or so. This geometric mean figure allows the beach to be graded into one of four categories: Grade 1 (Good), Grade 2 (Fair), Grade 3 (Poor), and Grade 4 (Very Poor). Any single sample that shows current E. coli levels exceeding 1,600 per 100mL overrides the geometric mean figure and immediately triggers a Grade 4 rating. This means the beach grading system can take into account rapid fluctuation in water quality caused by sudden events like heavy rainfall or localized pollution.