Idaho in Action / Aquatic Noxious Weeds / Hydrilla

Hydrilla Management

Hydrilla (Hydrilla verticillata) is one of the most aggressive and environmentally disruptive aquatic plants in the world. This invasive plant forms dense monocultures that restrict water flow, degrade water quality, impede recreation, and out-compete native species.

Hydrilla has been referred to as the “perfect aquatic weed” because of its ability to dominate aquatic systems through efficient propagation and colonization. Due to these characteristics, the identification of hydrilla in Idaho is of particular regional concern because of the potential to spread downstream into the Snake and Columbia River systems.

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Idaho Hydrilla Locations

Hydrilla has now been identified in four locations within three southern Idaho counties (Owyhee, Ada, and Twin Falls). The first population was identified in the Bruneau River near Bruneau, ID in December 2007 with a second population discovered shortly after in a North Boise neighborhood in 2008. Routine surveys in Twin Falls County led to the discovery of a third population in 2015, followed by additional locations within the same county in 2016 and 2017. All infested areas are located within surface waters which have geothermal influence. The area of mixing created at these ambient water/geothermal water interfaces create habitats with suitable temperature ranges for hydrilla growth and establishment. Temperatures required for optimal growth of dioecious hydrilla range between 20C and 27C and are temperatures that can be found year-round in several of these sites.

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+ Photo Credits

Images: ISDA Staff / Map: ESRI