Albert Barnes Commentary Psalms 89:25

"I will set his hand also on the sea, And his right hand on the rivers." — Psalms 89:25 (ASV)

I will set his hand also in the sea ... - His dominion will extend from the sea on the one hand to the rivers on the other. The sea here evidently refers to the Mediterranean; and the rivers to the great rivers on the east—the Tigris and Euphrates. These were the promised boundaries of the land (Genesis 15:18). David secured a conquest over all these territories, and united all under his scepter, thus securing the accomplishment of the promise made to Abraham. See the notes at (Psalms 60:1–12).