[6][5] It grows on muck, sedge peat, wet sand or silt, in filtered or full sunlight.

[6][5][9] Leaf blades are grayish blue to dark green, grow as long or longer than the stems, and are 8–20 mm wide.

[5] The female spikes are thick, 10–15 mm wide, and 2–10 cm long, either sessile (stalkless) or on short stalks, with 50–100 well-separated florets.

[14] Thin female scales are ovate (tapered at tip) and awned, translucent to purplish or brown in color, and half the length of the perigynia.

[5] 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.

[15][9][16] It forms scattered clones or beds, and sometimes extensive stands are seen without fertile culms[15][9] It is abundant and often a dominant plant of calcareous, north-temperate wetlands.

It does not naturally reestablish well in isolated wetlands restoration, likely due to limited water-borne seed dispersal.

It benefits from well-planned restorations with an aim of dense stands to preempt undesired aggressive species.

[3] The full list of US states is CT, DC, DE, IA, ID, IL, IN, KS, MA, MD, ME, MI, MN, MO, ND, NE, NH, NJ, NY, OH, PA, RI, SD, TN, VA, VT, WI, and WV, and the full list of Canadian provinces is AB, MB, NB, NF, NS, ON, QC, and SK.

[1] NatureServe ranks the species global conservation status as G5 (secure – very low risk of extinction or elimination).