skimmer question.

The simplest skimmer is a plastic box sat on a shelf with either the top of one side cut away or short enough that the entire top sits just below the water line. Suck or pump water from that and you will draw in surface debris. It would be best if you had some way of catching the debris especially if the pump sits in the box. The box also needs to be ballasted to keep it down.
During the build of my pond I used just such a skimmer to keep the surface clear. The photo shows it, the net is the strainer and the left hand side was cut down.
You can probably come up with something more appropriate than my set up but it did work