small leaf pond growth
Yes, looks like duckweed. You can manage this weed, but eliminating it altogether is very difficult because getting every tiny plant is hard.
Much depends on your pond. It is a small plastic lined insert? Are there other plants in the pond?
1. Wind-row method: Remove as much as you can with a skimmer either before or after you "blow" it all into one end or spot (a smooth edged area is good). You can use natural wind or use a fine spray hose to do this. You may need to do it more than once. Manually remove all that you can.
2. Treat with an herbicide. You must use one specially formulated for ponds and be careful to use one that does not harm fish if you have them. We assume this pond is not natural and flowing into waterways. In that case, you'll need a permit. It is easy to obtain by calling usually - Ed Gertler, 410-537-3651 at the Md Dept of the Environment. He may have useful advice also.
3. Some have tried "drawdown" or a partial draining of the pond to reach and treat the duckweed. With a small backyard form pond, you can empty, scour and refill.
4. Keep in mind that this plant can flower and produce seeds that can cause it to return no matter what steps you take.
The watershed specialist for Baltimore County may be helpful: Kelsey Brooks email@example.com