Simplify the following text for a Grade 7 native English-speaking person.
Original: While the river 's course and surroundings have remained almost entirely unchanged , the majority of it being protected by the Snowy River National Park , its flow was drastically reduced in the mid 20th century , to less than 1 % ( as measured at Jindabyne ) , after the construction of four large dams ( Guthega , Island Bend , Eucumbene , and Jindabyne ) and many smaller diversion structures in its headwaters in New South Wales , as part of the Snowy Mountains Scheme .
Simplified: Four large dams were built , at Guthega , Island Bend , Eucumbene , and Jindabyne , as well as many smaller dams and tunnels . Less than 1 % of the river flow , as measured at Jindabyne , New South Wales , continued to flow down the river .