In 2003, the California Department of Fish & Wildlife and the National Park Service breached 50 feet of levee that had isolated the 67‑acre Giacomini Dairy pasture, allowing tidal waters to flood the former pasture.
The inundation triggered a 143‑acre jump in salt and brackish marsh, raising the wetland’s salt‑marsh cover from 9 % to 37 % of the 400‑acre project area by 2018, the National Park Service reports.
Waterbird counts spiked, reaching 16,000 on a single day in December 2013, according to Avocet Research Associates; the peak fell to 10,000 the next year, stabilizing around 8,000–9,000 in 2017‑18. Green‑winged teal and American wigeon together accounted for 43.3 % of all waterbirds between September and February, the study notes.
The National Park Service now describes the Giacomini Wetlands as having entered a dynamic equilibrium, with native plant and fish communities stabilized, and a 2026 monitoring review scheduled to evaluate nutrient cycling.