This grower is sure of this plant identification.
Not suited to small ponds but excellent in larger ponds as a marginal or bog or waterside plant.
Carex pseudocyperus (Hop Sedge). This native sedge forms clumps of broad, lance-shaped to linear, green leaves. In late spring, drooping yellow-green flower spikes are produced, which later form brown catkins.
Plant with 10-20cm over the top of the planting basket.
Used as a marginal plant in larger ponds.