A great eyecatcher in your garden could be a fish pond or just a pond with water flora, bringing also tranquility to your scene, in particular when adding a water fall and/or a fountain to the whole.
Fish ponds, having a perfect eco-balance, can be build to any design, restricted only by your imagination. 
Flora ponds, having plants only or ponds with littlle fish can be maintained clean by simple sand filtration and a good balance of water flora.
Show ponds with (lots of) Koi karps will require much more sophisticated bio-filtration systems