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Yellow Flag Iris at Sweltzer Creek

Yellow Flag Iris at Sweltzer Creek

Posted Date: September 24, 2018

Sweltzer Creek has been the location for many projects for FVISS, including a native plant planting event in 2015. It is an important part of the area as it is the only outlet for Cultus Lake. This means that aquatic animals such as the endangered Cultus Lake Sockeye Salmon, use the creek to leave the freshwater lake for the ocean, and again to return and spawn. The creek is also important for maintaining water levels at the lake, and provide water flow downstream. The infestation of YFI has the potential of filling up this small but important flow of water for the lake.


YFI is an aquatic invasive plant that grows very quickly via rhizomes and seed. Manual removal of the plant is difficult, and any rhizomes or seeds that escape can float downstream and establish a new infestation. No chemical controls can be used since the plants are in water. YFI is a plant that modifies the ecosystem by collecting sediment and creating habitable space to grow even on rocky gravel beds. This can completely change the shallow water area, decreasing the area where waterfowl and other birds can find food, and lowering the amount of space that water can flow through. 

However, YFI is also a plant that will continue to try and metabolize when stressed, which has led to the development of a new YFI management technique by Dr. Catherine Tarasoff. FVISS staff had the opportunity to attend a workshop in June to learn the technique, and was able to implement this method this month! By cutting the plants to the base, and laying down benthic barriers to keep the rhizomes in a dark and anoxic environment, the plants' rhizomes are smothered until it uses up all its stored resources. Dr. Tarasoff's technique has shown success after leaving the barriers on for at least 70 days.

On a cloudy day in September, FVISS, volunteers, and Parks Board staff installed benthic barriers in Sweltzer Creek at Cultus Lake to manage the infestation of Yellow Flag Iris (YFI). It was a day full of hard work. Volunteers first began work by cutting off seed pods to avoid setting them free downstream. Then plants were cut down to the base, a thick black vinyl covering was laid out, and big heavy rocks were placed on top to weigh everything down. The site posed a couple challenges, including differentiating the YFI from Bulrush plants, swift currents and deep pockets of water that made certain areas of the creek inaccessible, and an area with a larger than expected infestation. After a day of sweat and blood (sedges can be sharp!), the barriers were installed, and now we wait. Stay tuned as we check on the barriers in the coming months!


This project was funded by the Vancity Community Partnership Grant. Thank you to all the fantastic Cultus Lake Parks Board staff, CLASS and UFV  student volunteers for all your hard work!