Potamogeton hillii is one of the small linear-leaved pondweeds that often present difficulties in recognition, but healthy specimens should be identifiable. The larger leaves of plants from the few Wisconsin locations appear to be in the range of 1.5 - 2.0 mm wide (although Flora of North America Vol. 22 reports 0.6 - 2.5 mm). The leaves are bristle-tipped, 3-veined (one fainter vein on each side of the mid-vein) and there is a narrow band of lighter cells on each side of the midvein. The peduncles are short (6 - 13.5 mm) and the spikes are very short (few- flowered) and nearly globose. A quick survey of achenes from the Wisconsin populations found the mature, dry achenes to be 3.4 - 3.6 mm long, but this is a very limited sample (FNA reports 2.3 - 4 mm). The lateral keels reported for the achenes of this species are less pronounced than the keys suggest.