The 36,000-acre Fish Slough Area of Critical Environmental Concern (ACEC) is a place where geographic isolation, geology, climate, and hydrology have created a rare and irreplaceable ecosystem. Located in the transition between the Mojave Desert and Great Basin biomes, Fish Slough encompasses an array of plant communities, including wetlands, alkali meadows, and uplands. With 126 taxa described, Fish Slough represents one of the richest wetland floras in the Great Basin. The ACEC also provides habitat for rare endemic plants, such as the Fish Slough milk-vetch and the alkali Mariposa lily.