Sparganium angustifolium is a species of flowering plant in the cat-tail family known by the common names floating bur-reed and narrowleaf bur-reed. It has a circumboreal distribution, occurring throughout the northern latitudes of the Northern Hemisphere. It is an aquatic plant, growing in water up to 2.5 meters deep. Its habitat includes acidic, low-nutrient freshwater bodies such as ponds, lakes, slow-moving streams, and ditches. It can become abundant, practically covering the surface of the water. It is a perennial herb producing a floating stem with long, narrow, flattened leaves which can be quite long, sometimes reaching over two meters. It is monoecious, individual plants bearing both male and female inflorescences. These are spherical, the male inflorescence a ball of stamens and the female inflorescence a ball of developing fruits.
- "Sparganium angustifolium Michx". Plants of the World Online. Board of Trustees of the Royal Botanic Gardens, Kew. 2017. Retrieved 23 December 2020.
- BSBI List 2007 (xls). Botanical Society of Britain and Ireland. Archived from the original (xls) on 26 June 2015. Retrieved 17 October 2014.
- USDA, NRCS (n.d.). "Sparganium angustifolium". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 24 November 2015.