Twenty milliliter of water from rice paddy fields and fresh water ponds was collected in six provinces locating around central part of Thailand: Nakornsawan, Chainat, Singhburi, Angthong, Ayuthaya, and Pathumthani. By re-streaking technique, a total of 210 isolates were obtained from 12 natural water sources. The biohydrogen evolution of each isolate was measured and plotted in the same graph with a unit of μmolH2/mg chl a/h as shown in Figure 3.1