Carex lacustris, known as lake sedge (lucastris is from the Latin lacus, or lake), is a tufted grass-like perennial of the sedge family (Cyperaceae), native to southern Canada and the northern United States. C. lacustris us an herbaceous surface-piercing plant that grows in water up to 50 cm (1.6 ft) deep, and grows 50–150 cm (1.6–4.9 ft) tall. It grows well in marshes and swampy woods of the boreal forest, along river and lake shores, in ditches, marshes, swamps, and other wetland habitat. It grows on muck, sedge peat, wet sand or silt, in filtered or full sunlight.
It's a common sedge that dominates many native wetlands, or intermixes with other sedges and grasses, and its ability to spread by rhizomes makes it a good colonizer for a large area.
Where it grows
C. lacustris is found in shallow marshes, marsh edges, shrub-carrs, alder thickets, wet and open thickets, open swamps, wooded swamps, sedge meadows, ditches, and borders of lakes, ponds, bogs, fens, and streams. It forms scattered clones or beds, and sometimes extensive stands are seen without fertile culms It is abundant and often a dominant plant of calcareous, north-temperate wetlands.
Text excerpted from the Wikipedia article Carex lacustris by its contributors, under CC BY-SA 4.0; the excerpts are shared under the same licence.
Life form, climate and native range: World Checklist of Vascular Plants, Royal Botanic Gardens, Kew (CC BY 3.0), reformatted; see Plants of the World Online.