Yangzonghai Lake and Dianchi Lake are two fault lakes among the nine plateau lakes in Yunnan Province, China. The former is a deep water and oligotrophicated lake, while the later is a shallow water and eutrophicated lake. The ecological factors, and the amount and structure of purple nonsulfer bacteria (PNSB) of these two lakes were studied in the even water season in 2002. The ecological factors included DO (dissolved oxygen), SD (Secchi disc), TN (total nitrogen), TP (total phosphorus), COD (chemical oxy...