Also, inb4conan.

for being first to put that in op
honestly this looks rather ugly to me. The shaping of the lake looks too roundish and man-made/shaped, though its not too discountable as a natural lake shape. Probably looks bad because relative to the river size, its puny. I'd go for a rough 1:20 ratio between river width and lake diameter, though expanding the river slightly before hitting the lake is a good idea.
The river is fine, but the bottom doesn't slope out enough imo. However, not all rivers are the same, and not all have nice smooth sloping.
Also, the level of the river relative to the lake makes it unsure which way the water is flowing; I'd adjust the height of the lake to lower than the river, and then have a small waterfall drop or gradual sloping down to connect the two.
You also should have done peripheral flat brickscape before posting; it looks too ugly and incomplete without.
I can't give a rating with what there is here; when there's flat terrain I'll reconsider.