Technical Abstract: Invasive, exotic aquatic plants impact a range of important economic and ecological functions in the Sacramento-San Joaquin Delta of California, and the state now spends over $5 million to control water hyacinth and Brazilian waterweed. In 2007, a new exotic floating plant South American Spongeplant (Limnobium laevigatum) was discovered in the San Joaquin River, which flows into the Delta. This non-native plant has also been found in small colonies in the Delta since 2007. It had been first found in a small impoundment in California in 2003, but its rapid clonal growth, reproductive rate, coupled with small, floating seedlings suggest a very high dispersal potential of this species in the Delta. This new pest poses a serious threat to the navigation in Delta waterways, may impede water delivery to 20 million Californians, and may further stress endangered fish species in the Delta. USDA-ARS and California Department of Agriculture are taking rapid response actions, including physical removal of small colonies, and identifying effective herbicides. Research to develop long-term management using biological control is planned by USDA-ARS through collaborations with its South American Biological Control Laboratory in Buenos Aires, Argentina.