Uncommon, in lochs
Leaves c 5-20 cm long, c 0.25-1.5 mm wide. Fruit c 3-5 mm long, 2-4 mm wide.
ID: Stipules in two parts, first joined to the leaf and forming a sheath, then at the top of this sheath a projecting ligule. The effect is rather like that of a grass leaf with its sheath and ligule. To distinguish from Slender-leaved Pondweed fruits are necessary. In the present species they have one side almost flat and the other very rounded, so that the beak of the fruit is well over to one side (see bottom left pic). In Slender-leaved both sides are rounded and the beak is almost in the centre, also the fruit is smaller, no more than 3 mm tall and 2 mm wide.
Other features: This species and Slender-leaved Pondweed form a group different from the other pondweeds in that the spike has the fruit much less dense and sometimes rather gappy. The spikes remain underwater and the pollen is carried from flower to flower by water. In the main pondweed group the spikes are emergent and wind-pollinated.