When you create holes using terrain tools so you can add lakes/water beds etc, it would be great to be able to fill up those holes right up to the top, with water, using the water tool. When you try to though, it will only show a red line of where you want to fill up the hole to, if you want to fill it up to the top of water. You can only fill holes up to where the blue line permits. I wish frontier changed this. This also happens in Planet Coaster too.