The zoo wants to add 54 acres of undeveloped Knowland Park land to build a veterinary hospital, new animal exhibit, camping area and educational center.
The Oakland Tribune reports that the lawsuit by the California Native Plant Society and Friends of Knowland Park argues there were flaws in the environmental review process when the city council approved the plan last month.
Environmentalists say they want to protect threatened animal species and rare native plants on the undeveloped park land.
