Welcome BBQJustin!
You can pump out the water and hopefully let the pond basin dry out to where you can excavate a lot of the silt out, however, you may have troubles with rain if it prohibits you from working with earth-moving equipment.
If you were to use an excavator with a long boom, you could get out some of the muck, but not all of it as the reach probably wouldn't get to the center (assuming the shape of the 1/2 acre pond is circular).
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