Two counties in California and an environmental group have partnered together to file an appeal against Southern California’s biggest water supplier, blocking its purchase of the Delta farm islands.

Contra Costa and San Joaquin counties, along with Restore the Delta group, have sued Metropolitan Water District in an attempt to stop its plan to buy the islands, which comprise 20,000 acres of wetlands. The group said the plan is an attempt at a water grab to move Delta water to Southern California.