Perennial sedge to 2m tall. Leaves alternating up the stems, with a sheath at the base, about 50cm long, 6-11mm wide, flat, grass-like. Spikelets 10-20mm long, red-brown or yellow-brown, with leaf-like subtending bracts, with 0 petals. Flower clusters at the tops of the flowering stems, umbel-like, with 4-6 branches bearing clusters of 1-6 spikelets, subtended by 2-6 leaflike bracts 15-25cm long. Grows in water.
PlantNET description with line drawings: http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Bolboschoenus~medianus