Thanks for all the advices !First off, that Zoo looks fantastic!!
You can find your save file here:
%USERPROFILE% \Saved Games\Frontier Developments\Planet Zoo\ <user-id> \Saves
You can send it to Frontier, not sure if it's either support@frontier.co.uk or community@frontier.co.uk.
I am not sure if they can save the file. But it could be real helpful to them to understand the issue.
The fact the game crashes when deleting the water, tells me, either the (local installation of the) game is broken, or the save file.
I don't think the "lake" you created is the issue.
Have you already tried verifying game files?
Last question, I don't want to take your time more : what do you mean by "verifying game files"?