The first step is to go out with your shovel and determine how much material you need to remove from the pond.

The infilled sediment and organic matter should look quite a bit different than the bottom of your pond.

Dig at the deepest "quiet water" portion of your pond (when it had water), which will probably be near the front of the dam. That should give you a figure for your deepest fill. Also dig on a gentle slope where the prevailing wind typically moves your pond water. That should give you a figure for you shallowest fill.

After you evaluate the size of the job, then you can more easily pick the best tool for the job.