Pumping isn't an option and filling isn't an option...Well that's pretty limiting but if the pond is above the surrounding landscape like when a berm is used to build a pond, then the berm can be torn down in a spot to let water drain away.

I assume this isn't a pond you have to keep adding water too because the answer would be pretty simple.

If the pond was built in a low spot where you get rain and/or snow you're up against the laws of physics. You'd have to build a roof over the pond to keep out the water. Kind of silly for 1/3 acre.

If the pond was built where there's a high water table or is spring fed even pumping wouldn't work. Unless big pumps running all the time were used.

If this pond was scraped out of the low spot the soil removed is still likely still there, even if it isn't apparent. A dozer can be hired to push the surrounding soil back into the pond. It might mean scraping something like 1 acre to fill 1/3 acre. And the result might still be a low spot. Some ponds are made as the cheapest way to get rid of a marsh type spot.

You don't say where you are, but if it is a natural pond, not man made, there may be enviornmental laws about messing with it. I don't know what the size requirements are but you might want to check with your county extension service before messing with it. We ran into this with a piece of property we were going to buy.

Hmmm...

If the pond is the result of water run-off, maybe build a "water garden" at the start of the pond, and maybe the plants will eventually "suck up" all the water?

Here is a link that might be useful: Building a Rain Garden

Solomon,
Don't mess with it until you speak with the county.
The poster above was correct.
There is a very good chance you have an underground water scourse, or stream for that NATURAL pond.
You could get in trouble, believe it or not, by messing with that pond.
Or something worse, if it is a stream.