Water Cycle - Oceans (5)
Post Lab 

  • Exploring estuarine systems.
  • Discovering the San Francisco Estuarine System.
  • brackish
  • estuary
  • worksheets 

Students use a worksheet to explore the San Francisco Bay Estuary.

Estuary near Sugar Dome in Brazil.


The San Francisco Bay estuarine system is a complex of interconnected embayments, sloughs, marshes, channels, and rivers.  The Bay system is comprised of the Delta Area (north), receiving the waters of the Sacramento and San Joaquin river systems and the San Francisco Bay proper (south), into which the Delta waters flow.  Geographically and hydrodynamically the estuary can be divided into the northern bay, which passes south, and westward from the Delta through Suisun and San Pablo bays, and the south bay which extends southeastward toward San Jose.  They join in the central bay near the Golden Gate, the connection with the Pacific Ocean.

The waters of the San Francisco Bay are a mixture of the salt water flowing in from the Pacific Ocean and the fresh water flowing from rivers that feed into the bay.  The water in the bay is neither salty nor fresh, but brackish.  This entire system is known as an estuary.  The San Francisco estuarine system is made up of three bays:  San Francisco in the south and the San Pablo and Suisun Bays in the north.  There is only one outlet to the Pacific Ocean for all 3 bays, a small opening underneath the Golden Gate Bridge (connecting San Francisco and Marin).  The force of tides (caused by gravitational attraction of the Moon and Sun) causes water to move into and out of the bay.  The influence of this mass movement caused by the tides flushes the estuarine system. 

The San Francisco estuarine system is a very productive area.  It is important to the entire ecosystem of the western United States.  Many organisms depend on the bay for food, safety and shelter.  Migrating birds need to rest here on their trips to warmer climates and nest during breeding seasons.  The animals in the estuarine system are varied.  Mammals, birds, reptiles, amphibians, invertebrates, protozoa, and fish are all components of this system.  The system has many parts to it because of the need of the larger animals to feed on the smaller animals.  This process is called the food chain and it give us clues to why animals eat and live where they do.

The bays today are very shallow, 85% of the water is less than 30 feet deep.  There are deep, narrow channels that cut the bottom of the bay,  the Golden Gate (about 400 feet deep) and the Carquinez Strait (about 100 feet deep).  Circulation of the bays is dependent mainly on the strong tidal action, especially in the south bay and river inflow, especially in the north bays.  Winds, storms and bottom topography change these patterns locally. 

Salt marshes of the San Francisco Bay area are highly productive and extremely valuable to the bay's ecology.  Salt marshes contain a variety of plants, but there are only a few common to all California salt marshes.  The plant groups occur in four distinct zones due mainly to the amount of salt in the soil, texture of soil, rates of sediment deposition, and the length of submergence.  The specific location of each zone changes in response to time of the year and environmental conditions, but their relative positions remain the same.

Some of the most common plants found in the salt marshes are the following.  Salt bush is a common low shrub of the salt marshes.  These are hardy plants with numerous seeds and are tolerant of the salty soils, commonly found along disturbed areas such as roadways.  Salt grass has long and narrow grass like leaves growing out from its stiff and erect stem and is about one foot in height.  Cordgrass is a perennial, that dies in the fall, that can tolerate many hours of submergence.  It reaches a height of over 4 feet with long and narrow leaves.  It's system can rid itself of the salt, by filtering the salt out and the salt crystals form on the leaves.  Pickleweed has stems that are pickle like in appearance and are attached end.  The leaves form scales on the joints of the uppermost segments.  Its leaves do not excrete salt but absorb it.  In the fall the "pickles" turn red, dry up and die.

The San Francisco Bay has evaporative ponds that produce salt for commercial markets.

  1. Oceans and land meet in different ways.  An estuary, which is a place where salt water meets fresh water is a habitat that is full of organisms living in a dynamic oceanographic system.  If you live near an estuary you should find information about that area and the importance in area.  Estuaries usually act as a filter to help naturally sort nutrients and sediments from water before it goes out to the ocean.
  2. The east coast has many estuaries compared to the west coast.  This exercise looks at the San Francisco Bay Estuary system.  Students are to look at the geographic setting and try to determine where the fresh water turns into brackish (partly salt) and then to full saline water
  1. (1) Dumbarton Bridge
    (2) San Mateo Bridge 
    (3) Bay Bridge 
    (4)Golden Gate Bridge
    (5) San Rafael-Richmond Bridge
    (6) Carquinez Bridge
    (7) Bencia Bridge   
  2. There are 3 bays - San Pablo, Suisun, and San Francisco Bay.  The San Francisco Bay is the largest. 
  3. A peninsula is land surround on three sides by water.  The land that the city of San Francisco is on.  
  4. Brackish water is where fresh water meets salt water which would be in the Suisun and San Pablo Bay.  
  5. Pacific Ocean.  
  6. Sacramento River.  
  7. The salt marshes are in the southern part of San Francisco Bay and in some areas in San Pablo Bay. 

  [Back to Water Cycle Grid]  [Back to Oceans (5)]