The amphipod Crangonyx floridanus and the isopods Caecidotea racovitzai and Asellus hilgendorfii were discovered in the Sacramento/San Joaquin Delta, California, U.S.A. We applied Chapman and Carlton's (1994) criteria for determining introduced species to test whether these species are non-indigenous to the delta. The majority of the attributes scored positive, indicating that these species are non-indigenous. These populations appear to be firmly established, as they occurred at a variety of freshwater wetland habitats throughout a one-year study. The species are briefly described, and distinguished from similar native and non-indigenous species known to exist in the surrounding area.