Few things
- Water is experimental, an excuse for not fixing it in past almost 3 years.
- This has been reported in so many other posts. Mods normally will not look into your posts, if it doesn’t have enough votes, So if you see a bug that you have also encountered, vote for it. This post only has 2 votes and one is mine!
- One that I could find immediately is this post. Apparently editor tries to load your entire landscape at once and if you don’t have enough memory it will crash your system
- There is an active bug report about modifying the landscape in anyway (including adding water body to landscape) causing crash, in Issue tracker which happens on Radeon graphic cards which is active for over 3 years to, (Not your case I assume).