Formal designs can have curved designs and be in-ground like the one here You can also include a patio and walkways. Giving the koi pond a modern design..
The cool thing about a formal design is that you can include seating, and raise it up off the ground. This makes viewing and taking care of the pond easier.
A well-done natural looking koi pond is hard to beat. The boulders and plants will often add more dimension than a formal design. Bringing everything to life and making you feel like you’re in paradise.