The occurrence of algal bloom has threatened the water quality of Taihu Lake that provides drinking water for millions
of people in the eastern Chinese city of Wuxi, Jiangsu Province. Chlorophyll a presented in living phytoplankton is a
very important ecological and environmental parameter of waters and it is usually used as indicator of the algal bloom.
To assess changes in chlorophyll a concentration distributions before an algal bloom in Taihu Lake on May 29,2007, a
linear model was established between the radio of band 1 (620-670nm) to band 2 (841-876nm) of the MODIS mediumresolution
bands and the <i>in situ</i> measurements of chlorophyll a concentration. The distributions of chlorophyll a
concentration are mapped. The phytoplankton patches are evenly distributed over the Taihu Lake during March 2007,
while the patches are confined to north part of the lake along the bank during May 2007, including Meiliang Bay where
the water supply of Wuxi city is. This study demonstrates that the moderately high resolution of MODIS/Terra 250-m
data is useful for monitoring the chlorophyll a distribution in small inland water body such as Taihu Lake.