Plankton in Baiyangdian Lake, China can tell us about the lake's health. By studying the types of plankton, scientists found that most of the lake is slightly polluted, with some areas more polluted. The main factors affecting plankton are ammonia, nitrogen, phosphorus, and oxygen levels. The lake's plankton diversity has decreased over time, and nitrogen seems to be the main cause of pollution. This means Baiyangdian Lake could become more polluted in the future.