Thanks LC

I've never really seen river water as being blue.

The sea and lakes are often blue, but a lot of rivers are various shades of brown with silt, or green with algae, or they might look green because of the abundance of water plants just beneath the surface. I've even seen a red river, which was polluted with metal oxides from an old tin mine. I've also seen a river that's a very very pale viridian - the dust of slate suspended in the water near an old Welsh slate quarry.

In this case I think the river is green because it is very clear, and there are lots of green plants growing in the water