Why don't you want to drain the pond? If you want to save the fish, that's understandable. But, 1/2 acre of fish can't have much dollar value. And, the cost savings of keeping your fish would be outdistanced by additional costs of using an excavator to deepen the pond. By draining, soils can begin drying, and your pond can be deepened by a bulldozer. A bulldozer pushes dirt efficiently, then spreads it quickly, mixing pond bottom silt with topsoil along the shoreline, or by pushing silt over the dam, where it can't run back into the pond. An excavator, on the other hand, has to dig the dirt, pile it up, then let soils dry. Then, another piece of machinery spreads the dirt, or hauls it off. So, if you use an excavator or dragline, expect to move your dirt twice.
Also, keep this in mind...the least expensive way to deepen a pond is to go up. Can you raise the dam two feet? If so, this move adds two feet of water, at considerably less expense.

Teach a man to grow fish...
He can teach to catch fish...