Simplify the following text for a Grade 10 native English-speaking person.
Original: The Kara receives a large amount of freshwater from the Ob , Yenisei , Pyasina , and Taimyra rivers , so its salinity is variable .
Simplified: The Kara receives a large amount of fresh water from the Ob , Yenisei , Pyasina , and Taimyra rivers , so its salinity is very variable .