This study was performed for the purpose of monitoring monthly levels of two pathogenic microorganisms, Cryptosporidium and Giardia, from November 2005 to August 2007 in Sangsa Lake. Water temperatures, pH and DO fluctuated seasonally at the study site. Annual mean values of BOD, COD and SS were $0.8;mg;L^{-1}$, $2.3;mg;L^{-1}$ and $1.9;mg;L^{-1}$ respectively. Although there was distinct seasonal variation in water chemistry and chlorophyll $underline{a}$ concentration, the lake generally contains low concentrations of nutrients and chlorophyll $underline{a}$. The relative abundance of coliform bacteria was always greater than that of fecal coliform. The fecal coliform bacteria comprised $8.5{sim}22.1%$ of total coliform bacteria. Seasonal analysis of Cryptosporidium and Giardia levels in the study site showed that in winter (November through February), Cryptosporidium oocysts and Giardia cysts were most abundant ($1.1{sim}1.8;{ imes};10;cells;L^{-1}$ and $3.8{sim}5.1;{ imes};10;cells;L^{-1}$, respectively), while in summer (July through September) the abundance was lowest ($0.0{sim}0.3;{ imes};10;cells;L^{-1}$ and $0.9{sim}2.9;{ imes};10;cells;L^{-1}$, respectively). Molecular identification revealed two subtypes of Cyrptosporidium parvum in Sangsa Lake.