I had to ask my pal at gw as he loves to add water to his bases haha
Step by step:
Base: Regal Blue
Layer 1: Sotek Green
Dry Brush: Temple Guard Blue
Dry Brush 2: Ceramite White on the edges where the water meets the land and a very light dry brush overall.
Ardcoat Layer to give it a shine
Glaze Layer: Very light layer of Guilliman Blue
Ardcoat layer 2
Drybrush 3: Ceramite white on the edge of the river again
Arcoat Layer 3.
Finished
I plan to carry the river on down my larger based models. Tempted to make Tetto'eko base all water so his mount is hovering over a ruin in the water.