page_title: Rodeo Lagoon
section_title: Inflows and outflows
hierarchical_section_title: Rodeo Lagoon / Inflows and outflows
caption_attribution_description: Pedestrian Bridge at Rodeo Lagoon and Rodeo Beach, viewed from near the Fort Cronkhite parking lot. The lagoon was not connected to the ocean at the time.
context_page_description: Rodeo Lagoon is a coastal lagoon located in the Marin Headlands division of the Golden Gate National Recreation Area, which is in southern Marin County, California. This brackish water body is separated from the Pacific Ocean by a sand bar that forms Rodeo Beach. Rodeo Lagoon stretches approximately 900 metres by 250 metres, and is about 2 metres deep at its maximum depth. It covers a surface area of about 15 hectares.
context_section_description: Rodeo Lagoon empties into the Pacific Ocean when the water level reaches a high enough level to erode through the sand bar.  This high water level usually occurs in the winter months.  The outlet channel, shown at left looking southeast towards Rodeo Lagoon, is spanned by a pedestrian bridge that provides access to Rodeo Beach.  Like many other coastal lagoons in California, the outlet becomes completely blocked by a sand bar during the dry summer months, resulting in negligible exchange between the lagoon and ocean during that time.
  The depth, surface area, and volume of the lagoon all vary depending on the configuration of the sand berm (high or low) and rainfall (wet or dry).  Depths in the center range from less than 1.5 metres (4.9 ft) in a dry summer to nearly 3 metres (9.8 ft) in a wet winter.
  Tides do not have a significant effect on the circulation of water in Rodeo Lagoon.  Instead, the circulation of water in Rodeo Lagoon is driven almost entirely by the wind.  Since the Marin Headlands are often quite windy, it is not unusual to see Langmuir circulation form windrows of foam on the surface of the lagoon.
  Rodeo Lagoon is a brackish water body, with salinities in most of the lagoon ranging from 2 to 10 practical salinity units (psu) over the course of the year.  However, water near the bottom of the lagoon is often much saltier, reaching levels as high as 25 psu.  The bowl-shaped bathymetry of the lagoon traps this dense, salty water and prevents it from quickly draining back out in the ocean.
caption: Outlet channel of Rodeo Lagoon
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