Simplify the following text for a Grade 3 native English-speaking person.
Original: The dam forms the Tarbela Reservoir , with a surface area of approximately 250 k. The dam was completed in 1974 and was designed to store water from the Indus River for irrigation , flood control , and the generation of hydroelectric power .
Simplified: It has a reservoir size of 250 k. This makes it the largest earth filled dam in the world . The dam was completed in 1974 .