It is not really a tut because it is a mix of previous tutorials.

The first you need is AllHeartAnne one : How to build a pool in a lake

Second is AphexZero one : Building an Aquarium pool in S3.

First are the pond, the house and the pool following the previous tuts.

Then, ConstrainFloorElevation False , enlarge the pond starting from it with the small brush using smoother pencil (it is easier and safe)

Try to stop your work sometimes, just to have an undo point in case of mistake.

At this point you can flatten the bottom of le pond.

I did this example whith an level 0 room for screenshot reasons, of course you can make it with a sunken room. Just to show I use the two ways to connect the pool/pond to the wall.

Thats all for the building phase.

You can start with the deco using the MoveObjects On an Alt key to be free from the grid to place various rocks, plants, recoloured carpets... on the blue pool bottom to mask pond hedges, recolor pool walls...

Halas my simmies can't swim from the pool area to the pond.

may be you find how to... let me know !

thank you

that's really nice tut xD

So we can make the pool area bigger and also build the pound?

It is not a matter of size, you can mix a pool and a pond where you want, as you want

Do sims swim in the pond or stay where the swimmingpool was??