The Natural History of Foster City, California

by James K. Sayre

a draft manuscript

12 May 2005

Chapter 3 - Operation of the Lagoons

The system of lagoons, which provide great beauty and interest in Foster City, were initially created primarily to provide for storm drain runoff from the winter rains and to provide a method of defense against possible flooding due to a combination of high tides combined with runoff from winter storms. The main channels of the lagoons were created to be about six feet deep at the maximum (although the large area next to .i.Ryan Park; may be somewhat deeper). The main lagoons vary in width from about two hundred feet to about a thousand feet in the area of Ryan Park. The total surface area of the lagoons is over two hundred acres. The volume of water held in the lagoons is typically about 424 million gallons, although this quantity can vary with the level of the lagoons. The inlet for the lagoon system is located on the .i.Belmont Slough; in the southeast part of the City. The inlet is controlled by valves that allow water in at the high tide times and close it off at other times. The outlet goes into the San Francisco Bay on the northwest part of the City. The outlet has a series of electrically controlled pumps to augment the gravity outflow (at low tides). Each week the lagoon water level is lowered at the beginning of the week (Monday, Tuesday and Wednesday) by the pumping of the water back into the Bay just north of the San Mateo Bridge. Thursday, Friday and Saturday new bay water is drawn in at the inlet on the Belmont Slough.

The level of the lagoons is raised each spring in the middle of March to its higher summer levels. This higher level allows greater use for sailboats and other recreational users of the lagoons in the summer months. These levels are lowered in the middle of November [Islander, pg. 4, 3-27-96].

The City of Foster City had a .i.Lagoon Management Plan; prepared in 1992 [City of Foster City, 1992]. Section 4 of the Plan discusses several water quality problems and their potential solutions. One problem is the annual spring and summer growth of a native aquatic plant, .i.Widgeon grass;, .i.Ruppia maritima;. City workers put a chemical .i.herbicide;, .i.Aquazine; into the waters of the lagoon. This herbicide also controls the growth of two species of .i.algae;, .i.Chadophora sp. ;and .i.Enteromorpha sp. Aquazine is usually applied in late May.[Foster City Islander, 5/22/96]. Beaches that have had this herbicide sprayed on nearby waters are posted "No Swimming" for the day of the application.

In 1980, two State of California workers from the Pesticide Investigations Unit, Environmental Services Branch, Dept. of Fish and Game took measurement of a pre-emergent herbicide, .i.dichlobenil;, which was applied to the lagoon waters [Finlayson, Lew]. They took measurements of dichlobenil and its metabolites in the lagoon waters, in lagoon bottom sediment, in .i.Softshell clams;, .i.Mya arenaria;, .i.Japanese littleneck clams;, .i.Tapes japonica;, in .i.Bay mussels;, .i.Mytilus edulis; and in .i.Pile surfperch;, .i.Damalichthys vacca;. In samples taken at thirty days post-herbicide-application, water concentrations of dichlobenil in the Lagoon and nearby Bay waters varied from 1.5 to 18 micrograms/liter. Note: a .i.microgram; is one-millionth of a gram. The concentration of chlobenial in shellfish and fish after thirty days past the application varied from 320 nanograms/gram down to less than 50 nanograms/gram. Note: a .i.nanogram; is one-billionth of a gram.

Children sometimes wade and swim in the interior lagoons where the water temperature in the shallow areas can reach as high ad 75°F in the summer. Because the general public may be exposed to water-borne diseases, Foster City tests its lagoon water quality once a month and twice monthly during the summer months. There has never been a serious water pollution problem, although about two years ago the beaches on the lagoons were closed to swimming for two weeks as a precaution, due to the rise in the coliform bacteria count, which was caused by an accidental overflow of a sewage line.

To deal with a reoccurring algae problem in the lagoons, each summer the city puts an algae-cide chemical into the waters. After the algae-cide does its job, it is considered inert and harmless and goes into the bay when the lagoon water is partially drained out (which usually happens on a weekly basis).

A small fish, the .i.yellowfin goby;, .i.Acathogobius flgrimanus;, has made itself a home in the waters of the lagoon. This fish, also known as a "mudsucker" is about half a foot in length. The goby, originally from Asia, was introduced into the waters of the Bay Area about thirty years ago. The Foster City Council banned commercial fishing in the City's lagoons on 2/6/95 [Jones].

In recent years, there have been some small jellyfish that have shown up in the waters of the lagoons. These may be .i.Moon jellyfish;, .i.Aurelia aurita;. They are close to colorless and their tops are only a couple of inches across. Apparently they do not present a danger to people.

End.

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