The researchers studied the phytoplankton in the Barje Reservoir in Serbia over a few years. They found that the reservoir changed from having mostly Bacillariophyta in 1996 to having more Bacillariophyta and Pyrrophyta in 1998/99, indicating it became more nutrient-rich. By 2001, there was less phytoplankton overall, but Cyanophyta started to appear, showing signs of eutrophication.