Baykeeper Update

Examining Ammonia Discharges to the Bay

To better understand how much ammonia is being discharged into the Bay from over 40 wastewater treatment plants that serve the towns and cities of the Bay Area, Baykeeper created an interactive map showing the scale of ammonia inputs from treatment plants to the Bay and its nearby tributaries. Ammonia is a form of nitrogen toxic to aquatic ecosystems at relatively low concentrations and is a common pollutant associated with wastewater released from municipal treatment plants following treatment.

Ammonia (NH3/4+) can impact the nervous system of fish and cause toxicity to organisms near the bottom of the food chain. Research conducted in San Francisco Bay has found that ammonia contributes to moderately toxic conditions within sediments at some locations. Other impacts associated with nitrogen enrichment, such as elevated chlorophyll and reduced dissolved oxygen is seen as a looming problem, particularly in the southern reaches of San Francisco Bay.

In the Delta, water quality impacts from the Sacramento wastewater plant’s ammonia discharges are severe enough that regulators have required the plant be upgraded to reduce ammonia concentrations. In addition, recent research indicates that phytoplankton production in that area of the Delta is limited due to elevated ammonia concentrations. Phytoplankton is necessary for the maintenance of a healthy San Francisco Estuary.

Regulators for San Francisco Bay are now pursuing investigations and processes to determine if the Bay is severely impacted by ammonia and other forms of nitrogen and phosphorus. Baykeeper is engaged in the Nutrient Numeric Endpoints (NNE) project, and we are following the results of scientific investigations to determine if changes in wastewater treatment are necessary to protect the health of the Bay. Though it is recognized that wastewater is just one stressor to the San Francisco amongst others, including municipal and industrial stormwater, non-native species, loss of wetland habitat, and reductions in freshwater inflow from the Delta.

To create a map of ammonia discharges to the Bay, Baykeeper used information from self-monitoring reports submitted by the treatment plants, and made available by the State Water Board. Not all treatment plants are required to report their ammonia discharges, making it difficult to determine how much of the pollutant is released into the aquatic environment. Based on the numbers available, the daily ammonia load from all local wastewater treatment plants is probably around 40,000 kilograms, or about 90,000 pounds, per day.

This does not include ammonia inputs to the Delta or other upstream areas, a likely cause of significant impacts to the Delta and Suisun Bay. The largest upstream wastewater treatment plant, in Sacramento, currently emits about 13,000 kilograms of ammonia to the Sacramento River each day. A number of smaller treatment plants are located throughout the Delta and its tributaries, though their contributions are minor in comparison.

Scientists have long known that ammonia has toxic effects, as well as chronic impacts associated with the nervous system. Toxicity to fish in fresh water has been observed at low concentrations of 0.068-2.0 mg/L NH3 and acute toxicity for marine species is in the range 0.09–3.35 mg/l NH3, depending on species, temperature and pH. At much lower concentrations, impacts to the nervous system cause fish to become less active, affecting migration, feeding and reproduction. Some of the region's larger wastewater treatment plants release millions of gallons of treated wastewater each day with ammonia concentrations as high as 40 mg/L.

As additional data becomes available, Baykeeper will provide updates and develop informative maps and information to serve the wastewater community and general public.


Eddy, F.B. 2005. Ammonia in estuaries and effects on fish. J. Fish Biology. 67(6):1495-1513.

Shingles, A., D. J. McKenzie, E. W. Taylor, A. Moretti, P. J. Butler, and S. Ceradini. 2001. Effects of sublethal ammonia exposure on swimming performance in rainbow trout (Oncorhynchus mykiss). Journal of Experimental Biology. 204(15):2691-2698.

Parker, A.E., et al. 2012. Elevated ammonium concentrations from wastewater discharge depress primary productivity in the Sacramento River and the Northern San Francisco Estuary. Mar. Pollut. Bull. 64(3):574-86.