'river mist' is a correct and usable phrase in written English.
You can use it to create a poetic or evocative imagery when describing a scene or setting. For example, "The morning sun glowed through the river mist, turning it into a dreamy haze."
A haze hung above the river, mist blurring the far bank still at 9 a.m.
The first thing I heard this morning, as I opened my eyes to bright sunlight filtering through the river mist, was the cuckoo - the first since last summer.
Dead Cert, published the following year, begins in mid-race: "The mingled smells of hot horse and cold river mist filled my nostrils.
On the porch of a moonshiner's shack, he has pressed his nose to a rusted screen, scratched it with his finger and seen his young father rise like river mist in the breath of the dying man inside.
The culatello they will become is aged in an ancient cellar, an intensely piggy, musty place with mouldering walls and river mists.
The objection was best put by HG Wells: reviewing An Outcast of the Islands (1896), he described Conrad's style as being "like river-mist; for a space things are seen clearly, and then comes a great grey bank of printed matter, page upon page, creeping round the reader, swallowing him up".
Here, underneath the music, there lie the mountains of my book, with their hills and rivers, mists and rains, the fires and their walkers, the storks nesting in the giant oaks.
The Grand Canyon of the Yellowstone gets the river-mist rainbows.
The tracks followed a narrow river valley, with mist rising up from the water and the sparkling grass.
And putting it -- and the future of the Congo -- together, he said, is like walking "on stepping stones in a river in the mist, where you can't see where the next step is".
When "Dr Vlad" arrives in Cloonoila, he sits by the river in the mist and listens to the sea and the screeching peacocks: had he read a few more novels and a little less Serbian nationalist poetry, he might even have recognised the place as an Edna O'Brien landscape.
