Install a surface aerator. Surface aeration can be anything from an agitator that splashes to an aerating fountain to a decorative fountain.
Install a bottom mounted diffuser with a compressor on the shore. The lines and diffuser rest on the pond bottom.
Install an aeration system in deep ponds of 6 feet or more. Use a subsurface aerator that churns the water from the bottom, bringing it to the top where it can be infused with oxygen. The deeper the pond, the faster the bubbles rise and the more water they circulate. A diffuser takes air and breaks it into fine bubbles. It's not so much the transfer of oxygen into the water from the bubbles as it is the water that these bubbles entrain and bring to the surface.
Build for aeration. If the pond is too be 6 or more feet deep, make arrangements for the bottom diffuser. For each quarter acre use at least 2 diffusers. If the pond is L shaped, put a diffuser at the end of each leg. If there is a shallow end, put the fountain there.