Is it possible that "playful" determines "river"?
I’m leaving early tomorrow morning, finally! I’ve always wanted to explore the Amazon, the unknown and mysterious world. At this hour, the great Emerald Amazon Explorer should be at the port waiting for me to get on board. Freshwater dolphins will escort me on the playful river, and 500 species of birds, half a dozen species of monkeys, and numerous colorful butterflies will welcome me into their kingdom.

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I wonder how the adjective "playful" , which indicates the mood of people, determines the word "river"?

Please help me!

Question

Is it possible that "playful" determines "river"?
I’m leaving early tomorrow morning, finally! I’ve always wanted to explore the Amazon, the unknown and mysterious world. At this hour, the great Emerald Amazon Explorer should be at the port waiting for me to get on board. Freshwater dolphins will escort me on the playful river, and 500 species of birds, half a dozen species of monkeys, and numerous colorful butterflies will welcome me into their kingdom.

---
I wonder how the adjective "playful" , which indicates the mood of people,  determines the word "river"?

Please help me!

Answer

As others have said it is personification, and for some reason it is fairly common to perceive a river as "playful" or "merry." To me, this suggests that the river is moving fast enough to make a pleasant bubbling noise, and to create small ripples and waves--but not to have dangerous rapids or waterfalls.

Answer

It is a figurative speech , a personification as mentioned above.
It is describing the river in the movement of its waves as a jolly lively person or kid maybe .

Answer

This is called "personification" which gives the attributes of a person to inanimate things, like a river. It is used to make the description more colorful. So we can imagine the dolphins playing in the river.