about rounded holes instead of suare... i am not sure, i really wish to know how and if it is possible.
about dig your own lakes :
1. i am not sure but i created a 200x200 water plane. but in game it is really not as 200x200. like if there is a limitation to 50x50 or 60x60 .. not sure.
2. you need to know the water has not any coloration , totally transparent. to get the blue effect, it comes from digging enough down to get the "blue" ground which kinda reflect on the water.
on the screenshots below you can see ontop of the river, the difference, it is not 200x200. you see it starting and see it ending.
on screenshot 2, you see the claypit and there is water there, hard to see on a picture cause the water is pure clear. the only thing in game you see is ripples and the wood planks are moving cause the water.
of course cause the plane is big, the water is very quiet and more hard to see. i would rather need to put more planes side by side instead of 1 giant plane in order to get thin ripples