When I add a Lake actor to my scene at transform (0, 0, 0), the edges stretch severely as seen in the first screenshot. This is resolved when I move it up approximately 100,000 centimeters, but of course this makes it unusable.
I tried moving my landscape up 100,000 units as well, but this bore the same result as before. I believe this may be caused by my Gaea Bleeding Edge heightmap, which required me to transform my landscape 20,000 centimeters, but I have no idea how to fix that.