Benthic algae a re one of the most important primary producers i n lotic ecosystems, and changes i n their community structure and function (e.g., metabolism) will influence other organisms at higher trophic levels or even the entire aquatic ecosystem through bottom-up effects. Since they are known to be sensiti ve to changes i n ambient conditions, benthic algae and especially diatoms have been widely used as i ndicators of environmental changes in aquatic ecosystems, particular ly i n E urope , through developi ng diatom-based indices. However, these indices have not been widely used i n other continents. Applications of such i ndices in Asia and Oceania first require testi ng to see whether the y can perform as reliable bioindicators across time and space, considering that aquatic systems are constantly changing in terms of their ambient environment such as water physical and chemical conditions. Nevertheless, few studies have been carried out to compare the environmental influences on benthic algal communities among different geographic regions, nor the influences at different spatial scales (e.g., catchment, reach, and habitat). F urthermore, few studies have considered how diatom indices perform compare with other commonly used bioindicators of aquatic ecosystem health.