Hard to tell...I would say the trees are too small, but only based on the sandy material on the shoreline. For a river, I would assume the "sandy" material wouldbe thin before grass jumps in. In your render, the sandy shore looks too big compared to the trees. But it's only my perception. How wide is your river? It lloks very wide here, compared to the trees. Now if a tree is about 6 meters tall, it seems here it would take about 3 trees to bridge the two shores, which would make about 18meters. A very wide river.