The purpose of this research was to assess water quality using physicochemical
measurements and benthic macroinvertebrates in the upper part of the Chi basin. Ten
sampling sites were established along the river course. Physicochemical and biological
properties were measured bimonthly. Twelve physicochemical variables of water quality
were examined and analyzed. The benthic macroinvertebrates were collected by
rectangular dip net kicking samples from February to December 2004. BMWPThai score,
ASPT, and HBI index were used to assess water quality. Relationships between sampling
sites and between seasons were analyzed by analysis of variance (ANOVA). Using of water
quality standard of Thailand, the results showed that the water quality of the upper part
of the Chi basin was in class 2-class 3 of the water quality standard which the condition
and beneficial usage of water quality was very clean freshwater resources - medium clean
freshwater resources. However, according to statistical analysis, these physicochemical
variables were not significantly different. Benthic macroinvertebrates of 8 orders and 25
families were found. The most abundant order was Odonata and the most abundant
family was Gomphidae. The water quality assessed by ASPT index agreed with the water
quality assessed by physicochemical variables. Whereas, the HBI index was not related to
physicochemical variables in most sites