Re: Pools with islands

@allisonlm13 As @Psychotps mentioned, it seems you're interested in creating a pool area around a land area, in which case you could just draw the pool it around a piece of land using the 'custom pool tool':

For example, I did this indoor to make this pool. Same principle, but the 'island' part in this case is flooring rather than land:


Also, if it would be helpful at all you are welcome to download the above lot and pick it apart to see how this type of pool is made:
https://www.ea.com/games/the-sims/the-sims-4/pc/gallery/2300886DA06111E989B3D5D7447C5F1D 

Can you clarify if you're looking for something different than we are mentioning? If so, can you add a screenshot/example of what you're trying to do?