It's long windy stems clog the waterways and get caught in boat engines.  The plant also harms Delta wildlife by blocking out sunlight and using up oxygen.

Boating and Waterways director Lucia Becerra says they're careful when applying the herbicide.

BECERRA: "Our treatment areas are very localized, so we use a pellet, and the pellete is sprayed right onto plants."

Becerra says they're spraying nearly 3,000 acres at a cost of about $5 million.

The weed is nearly impossible to eradicate, but she says the chemical does help clear the waterways, which benefits tourism.