Adam Clarke on Psalms 89:25

I will set his hand also in the sea - This was literally fulfilled in David. Hand signifies power or authority; he set his hand on the sea in conquering the Philistines, and extending his empire along the coast of the Mediterranean Sea, from Tyre to Pelusium. All the coasts of the Red Sea, the Persian Gulf, and the Arabic Ocean, might be said to have been under his government, for they all paid tribute to him or his son Solomon.

His right hand in the rivers - First, the Euphrates: he subjected all Syria, and even a part of Mesopotamia; 2Sam 8:3; 1Chr 18:3. He also took Damascus, and consequently had his hand or authority over the river Chrysorrhoes, or Baraddi; and in his conquest of all Syria his hand must have been on the Orontes and other rivers in that region. But if this be considered as referring to the typical David, we see that He was never conquered; he never lost a battle; the hosts of hell pursued him in vain. Satan was discomfited, and all his enemies bruised under his feet. Even over death he triumphed; and as to his dominion, it has spread and is spreading over all the isles of the sea, and the continents of the world.