I have an interesting question. In the NIV it says.
they flowed over the mountains,
they went down into the valleys,
to the place you assigned for them.
Psalm 104:8 NIV
But in another version it says
Mountains rose and valleys sank
to the levels you decreed.
Psalm 104:8 NLT
Do they mean the same thing? The NIV is talking about the water moving up and down and in NLT it says the mountains rose and valleys sank.
The Hebrew for Psalm 104:8 is:
ya'alu harim yerdhu veqa'oth 'elmeqom zeh yeasaadhta lahem
Literally this translates to:
(they went up) (the mountains) (they went down) (the valleys) (to the place) (this) (You allocated) (for them)
The translators for the New International Version decided that the "they" referred to the waters mentioned back in verse 6.
"He set the earth on its foundations; it can never be moved. You covered it with the deep as with a garment; the waters stood above the mountains. But at your rebuke the waters fled, at the sound of your thunder they took to flight; they flowed over the mountains, they went down into the valleys, to the place you assigned for them. You set a boundary they cannot cross; never again will they cover the earth" (Psalm 104:5-9 NIV).
The King James and the New King James avoid the issue by leaving it with "they" but implying that it refers to the waters.
"You who laid the foundations of the earth, So that it should not be moved forever, You covered it with the deep as with a garment; The waters stood above the mountains. At Your rebuke they fled; At the voice of Your thunder they hastened away. They went up over the mountains; They went down into the valleys, To the place which You founded for them. You have set a boundary that they may not pass over, That they may not return to cover the earth" (Psalm 104:5-9 NKJV).
Most of the remaining translations see "they" referring to objects in the immediate context, that is the mountains and the valleys.
"He established the earth upon its foundations, So that it will not totter forever and ever. You covered it with the deep as with a garment; The waters were standing above the mountains. At Your rebuke they fled, At the sound of Your thunder they hurried away. The mountains rose; the valleys sank down To the place which You established for them. You set a boundary that they may not pass over, So that they will not return to cover the earth" (Psalm 104:5-9 NASB).
"He set the earth on its foundations, so that it should never be moved. You covered it with the deep as with a garment; the waters stood above the mountains. At your rebuke they fled; at the sound of your thunder they took to flight. The mountains rose, the valleys sank down to the place that you appointed for them. You set a boundary that they may not pass, so that they might not again cover the earth" (Psalm 104:5-9 ESV).
What is being described is the great flood of Noah's day. The water covered the whole earth. "And the waters prevailed exceedingly on the earth, and all the high hills under the whole heaven were covered. The waters prevailed fifteen cubits upward, and the mountains were covered" (Genesis 7:19-20). But at God's command, the waters withdrew. "Then God remembered Noah, and every living thing, and all the animals that were with him in the ark. And God made a wind to pass over the earth, and the waters subsided" (Genesis 8:1). You can look at the withdrawal from the point of view of the water flowing away or see the effect of the waters receeding as the mountains became relatively higher and higher. Eventually the water settled into a level that it wouldn't rise above again. "Then the LORD said in His heart, "I will never again curse the ground for man's sake, although the imagination of man's heart is evil from his youth; nor will I again destroy every living thing as I have done. While the earth remains, Seedtime and harvest, Cold and heat, Winter and summer, And day and night Shall not cease."" (Genesis 8:21-22).
However, there is difficulty in saying "they" in verse 8 is the waters: we normally don't refer to water flowing up a mountain. And if we only focus on the water level, while it is easy to see how mountains rose, you can't see valleys sinking by the water going down. A better explanation, allowable in the Hebrew is that the method God used to contain the water was to literally raise the mountains and lower the sea valleys. Personally, I believe this is most accurate reading of the text.