 In the early 20th century, phytoplankton was dominated by green algae, diatoms, and carapace flagellates with a smaller amount of cyanobacteria, a normal distribution for lakes rich in nutrients.By 2000, the biomass was almost exclusively composed of cyanobacteria, most of them non-poisonous "thin filaments" and "anabacena" the only species being able to fixate nitrogen.Today, the only reminder of the 1990s is the relatively frequent occurrence of the carapace flagellate "Ceratium hirundinella".