Yellow Flag Iris is a highly invasive plant that forms dense stands in wetland areas, lakeshores, rivers, and streams. It outcompetes native species, disrupts water flow, and alters the natural structure of waterways. The plant can invade pastures, displace native vegetation, and is toxic to livestock. Its seeds are buoyant, easily dispersed by water, and can remain viable for over a year, making the plant difficult to control once established. Yellow Flag Iris negatively impacts the ecological health of water bodies, cultural values, and agricultural productivity.

Yellow Flag Iris is found across Otago, including Mosgiel, Lake Wānaka, Lake Whakatipu,  Lake Hayes, Tahakopa Estuary in Papatowai, and Oamaru. 

• Size: Yellow Flag Iris grows up to 1.5 metres tall. 
• Leaves: It has broad, flat, sword-shaped leaves that form a fan shape from the base of the plant.  
• Flowers: The bright yellow flowers are up to 12 centimetres in diameter, with three large sepals and three small erect petals.  
• Root system: The plant’s thick, fleshy rhizomes form dense mats and can float on the surface of water. 
• Similar species: It looks similar to Stinking Iris (Iris foetidissima), which has a foul smell when crushed, and Typha orientalis (Raupō), which has different flower heads and taller stems. 
• Habitat: Yellow Flag Iris is commonly found along the shores of lakes, rivers, wetlands, and drainage systems. It thrives in both fresh and brackish water environments. 

Yellow Flag Iris is most visible when flowering from October till December. 

Yellow Flag Iris is declared an Unwanted Organism in the National Pest Plant Accord.  Any species declared a pest under the NPPA cannot be sold or be in a place where plants are being sold. Pest plants cannot be propagated, bred, multiplied, communicated, released, caused to be released, or otherwise spread. 

Do not attempt to undertake control of yellow flag iris yourself. Report any sightings to Otago Regional Council.

www.orc.govt.nz/yellowflagiris