Abstract: This research was based on the data from 14 surveys on red tide monitoring areas of Sansha Bay from A-
pril to October in 2012. In this report the variations of physical and chemical factors and N/P ratio aie character
ized, the eutrophication status in aquaculture water are evaluated. The result shows that the water temperature, sa-
linity, pH value, dissolved oxygen ( DO) and chemical oxygen demand (COD) in the surveyed areas are suitable for the growth and breeding of marine organisms in the period studied. The contents of N and P, the most basic elements for phytoplankton growth, were high. The average contents of N and P are 0. 350 mg/dm3 and 0.041
mg/dm3. respectively. Geographically, the contents of N and P reach the lowest in the opening of Sansha bay and
they tend to increase from the opening to the inner bay and the bay head. Tlie variations are mainly affected by the 
terrestrial input besides aquaculture. The average of N/P ratio is 10. 7, the inorganic nitrogen (DIN) is low rela
tive to the active phosphate ( PO34-P).The average value of nourishment state index (E) is 3. 22, which exceeds 
the standard value by factor of 2. 22 and 87. 5% of measured values aie higher than 1. It shows obviously a rising
trend of eutrophication in contrast to the date from 1990 to 1991 when it was in a moderate eutrophication stale.