The researchers studied Lake Borovoe to see how healthy it is by looking at the tiny animals in the water called zooplankton. They found that even though there weren't a lot of nutrients or heavy metals in the water, the zooplankton showed that the lake is close to being too polluted. The number of zooplankton increased a lot, but each animal got smaller. The pollution mainly comes from the village of Borovoe and the resorts around the lake.