The aim of this project is to properly understand the changing trend of water quality in those types of water bodies that including “Major reservoirs,” “The other reservoirs” and “Major Rivers” of not only Taiwan main island but also offshore islands by the water quality monitoring. For the water quality and discharge investigation of “Major Rivers,” water quality monitoring was conducted once a month in twenty-four monitoring stations where located in twenty-one rivers. However, there were not all monitoring measurements could meet Class-A or Class-B criteria of“Surface Water Classification and Water Quality Standards”in all monitoring stations during monitoring period, especially on coliform group (58 %) and BOD5 (37 %), respectively. On the other hand, most of monitoring stations were categorized to non(slightly)-polluted level, there were only two monitoring stations categorized to light-polluted level, which may resulted from higher suspended solids concentration; furthermore, only two stations categorized to medium-polluted level, not only lower dissolved oxygen but also higher organic pollutants concentrations were observed in Gang Si pumping station. For the water quality investigation of “Major reservoirs”, water quality monitoring was conducted once a month in seventy-four monitoring stations where located in twenty-one reservoirs. The results showed that all “Major reservoirs” could not meet Class-A criteria of“Surface Water Classification and Water Quality Standards”, among these measurements over the standard, the highest ratio item was pH (31%), second, total phosphorus was 26%, and third DO was 21%, respectively. However, the results indicated that there was the highest proportion of oligotrophic ratings for the water quality of the Sun-Moon-Lake Reservoir (67%), on the contrary, 100% of mesotrophic ratings was observed for Lan-Tan Reservoir; furthermore, 100% 0f eutrophic ratings were observed for not only Mingten Reservoir but also Feng-Shan Reservoir. Compared to the recent five years monitoring, the decreasing Carlson trophic state index could be observed in Shimen Reservoir, however, the increasing trends (worse water quality) of Carlson index were found in Te-Chi Reservoir, Wu-She Reservoir, Tsengwen Reservoir, Pai-Ho Reservoir and Ching-Mien Reservoir, respectively. While the water quality changes during the monitoring period at the other reservoirs were within historical norms. For the water quality investigation of “The other reservoirs,” water quality monitoring was conducted once every season in thirty monitoring stations where located in thirty reservoirs. The results showed that the highest proportion of mesotrophic ratings for “The other reservoirs” of Taiwan main island, except for Ta-Pu Reservoir that being unable to sample resulted from full of Water Hyacinth on the surface of water during monitoring period, on the contrary, the worse water quality (the higher proportion of eutrophic ratings) was observed in “The other reservoirs” of Taiwan offshore islands, such as Kinmen County, Lienchiang County and Penghu County. Compared to the recent five years monitoring, the decreasing Carlson trophic state index (better water quality) could be observed in Houwo, Chu-Shui-Wo Lower Dam and Pan-Li Reservoir, respectively. The results showed that the other reservoirs were categorized to the eutrophic ratings for a long period without significant difference.

CTSI, Water quality, Reservoir, Carlson trophic state index , Major reservoir,Major River