Lean out of a boat in the Sacramento-San Joaquin Delta, grab a handful of plants or a net full of fish, and you’ll haul in a bunch of stuff that doesn’t belong there.
The Delta is considered North America’s most invaded estuary. About 200 foreign species have taken root here. A new one settles in about every nine months, usually when a cargo ship discharges ballast water or a homeowner dumps his aquarium in a ditch.
Ranging from Chinese clams and Atlantic fish to South American water weeds, they have crowded out native species in many areas. By some estimates, 95 percent of the Delta’s biomass, or the totality of its organisms, are not native.