|First off, make a pond. Depth doesn't really matter, but it shouldn't be too shallow.|
|Next, level out the bottom.|
|Then use the level tool thingy to reduce it to the size you want. Recommended minimum is 4x5, 3x4 if you are using two-tile seats.|
|Place your chairs (the sims must already be sitting on them). This will take a steady hand and a lot of patience. The benches should sort of be "perching on the edge" of the little pond.|
|Finally, add some plants and rocks and stuff to make it look realistic. Final result: This.|
Well, have fun!