Cambodian aquatic ecosystems are extremely diversified and constitute major preservation targets. However, the species composition, diversity, and distribution of the inhabiting algal communities are largely unknown. During a sample collection carried out in the Angkor and Banteay Srei monuments area in 2010, several unknown diatom taxa were found in various population densities in the artificial lakes surrounding these temples. Detailed light and scanning electron microscopy observations allowed the description of five of them (Pinnularia cambodiana, P. shivae, Gomphonema angkoricum, G. paradaphnoides, and Frustulia lacus-templi) as taxa new to science. Differential diagnostic criteria with respect to similar taxa, together with the ecological and environmental implications of these findings, are briefly discussed.