The researchers studied the types of tiny plants (phytoplankton) in Koprinka Reservoir in Bulgaria. They found 109 different types, with the most in September and the most variety in October. The area near the river had the most phytoplankton. In the summer, one type called Hariotina polychorda was common, and in early autumn, a potentially harmful type called Microcystis wesenbergii bloomed, showing the reservoir is getting too many nutrients. The different types of phytoplankton and their amounts show that the reservoir is becoming too rich in nutrients.