The “river of God” is a poetic expression for divine provision and inexhaustible resources. It may refer to the totality of fertilizing streams by which God waters and sustains the earth.
In Psalm 65:9 the expression contrasts God’s abundant resources with merely earthly streams and portrays the earth as nourished by his provision.
The image is associated with the river flowing from Eden, which watered the garden and divided into its branches.