The rivers that flow through Soomaa National Park play an important role in shaping the landscape. When rainwater or snowmelt water drains from the Sakala Highlands, the rivers of Soomaa cannot absorb it all at once, and the rivers that otherwise meander along the flat surface abandon their natural riverbed. The high water with its inundations is called the "fifth season" in Soo.aa. As a result of the flooding, the floodplain of Riisa is created, which can reach an area of up to 175 km² and whose water surface can be up to eight kilometers wide. On the board you can read some water levels from the last few years.