Most likely the very common white willow or black willow. I agree it's very invasive and a nightmare to control. I would caution planting it at your pond.
STRONGLY AGREE! I suspect they're black willows - a very aggresive invader. Mowing or cutting them usually results in 3-5 "suckers" (emerging from the root-crown) for every stem that is cut. Besides their invasive habits, willows transpire (exhaust) a LOT of water during summer months. Not so bad if you only have a few, or have plenty of rainfall to keep your pond full. But, not so good if you encounter a sustained drought.
Several herbicides are effective on willows, and using this option avoids the disturbance of shoreline-soils (erosion).
