Abbreviated Marsh History:

This Image Highlights the modifications made by the state in 1993.
*Click on image to enlarge.

Marshes usually have a continuous land form and high water table allowing for a saturated soil condition. The Pescadero Marsh has isolated pockets from levees, uneven land form and dredged channels changing the natural function.

*Some notable events occurring in the marsh are below in bullet format to reduce text:

• Farmers began building levees and drained small areas of the marsh by the late 1920s.  Substantial levee building and conversion of marshlands to agriculture occurred during the 1930s, and continued through the early 1960s. The Highway One Bridge was built in the early 1940s leaving remnants of a coffer dam road that may have raised the channel grade.  Intensive logging and watershed development, also beginning in the late 1920s or early 1930s, has increased sedimentation in Butano and Pescadero creeks.  Beavers documented in the lower channel in the 1950s reduced sediment movement through the system, especially since the late 1980’s. The floods of 1955 delivered large sediment loads to the marsh. Sediment continued to be introduced during significant storms such as 1982 and 1998 (ESA).

• The State began acquiring land in the 1960s. In the early 1960s local farmers used a dragline to remove sediment from Butano Creek channel below Pescadero Bridge for several thousand feet down stream. The sediment removed was used to build a 6,000 foot levee on the west side of Butano Creek. Other levees were built to keep salt water out of agricultural fields. (Cook). DFG required the dragline practice to stop following the introduction of new fish protection laws in 1963 (F&G Code Section 1600)

• In the mid-1980s a 25’ wide breach was made in the west bank levee of Butano creek approximately 50’ downstream of Pescadero Road Bridge. This breech may have reduced flood flows down the Butano Creek channel in the marsh and have been a factor in increased beaver activity/impact in the channel.  Breeches in other levees of the North Butano Marsh were also made to improve circulation (Cook).

• Concerns about agricultural pesticide runoff into the marsh prompted a report prepared for DPR by DFG (Jong; 1982). Jong confirmed eutrophic (high nutrient) conditions in the marsh and found that algae blooms raise DO levels to saturation during the day and deplete levels during night respiration. Jong speculated that the low night DO could result in fish kills. The DFG study found levels of pesticides potentially toxic to fish in the sediment.  (Jong’s study might have been more concerned with conditions in North Marsh and North Pond, rather than the main tidal estuary).

• Observations by Jerry Smith (1990) from studies during 1985-89 indicated that fish habitat quality of Pescadero Marsh was generally good but limited in extent if the bar was open.  Smith noted that early sandbar closure can reduce survival of salmonids if conditions are poor. In drought years when the inflows are low the closed lagoon will remain stratified, warm and brackish, fish blocked from migration by early bar formation will have poor survival. Poor WQ as measured by DO and temperature is created during stratified fresh/salt water conditions following bar closure. Growth and survival are best when the lagoon is open to tidal mixing or after the lagoon has converted to freshwater conditions. Smith determined that habitat quality depended on the quantity of freshwater inflows after formation of a stable sandbar. Rapid conversion of the lagoon to unstratified fresh water, supported relatively cool water temperatures and high dissolved oxygen levels optimal for fish and prey species Fish raised in the lagoon compared to the upper watershed during 1986 were larger and had denser populations. However, Smith noted that after early bar closure, high mid-summer temperatures and low DO can cause populations to disappear or at least relocate from many sections of the marsh. It appeared that the marshy sections of the system (North Marsh, Butano Marshes) tended to remain brackish and stratified longer and had earlier development of abundant pondweed. This led to more water quality (temp/DO) problems than the main embayment and stream arms).

• The Highway One bridge was rebuilt (1989-90) with fewer supports and closer to the ocean. Prior to bridge completion, Smith predicted that timing of sandbar formation would change.

• A hydrological enhancement plan (Phillip Williams and Associates) was completed for DPR in 1990. The main foci of this plan were to increase tidal prism, reconnect marsh areas to the stream and lagoon system, and relieve flooding of agricultural lands and Pescadero Road.

DPR’s stated management plan for the marsh is to return its 340 acres to near natural conditions through a series of projects calculated to reduce the affects of sedimentation, past levee building and farming. Additional goals are to improve listed species habitats for San Francisco Garter Snake (SFGS), California Red-Legged Frog (CRLF), Tidewater goby, and Steelhead.  Projects calculated to improve the hydrology were conducted after several years of studies as described in “Pescadero Marsh Natural Preserve Hydrologic Enhancement Project” (DPR 1992).  The low levee in North Marsh and the presence of culverts that could be adaptively open and closed were designed to address concerns that the increased tidal prism and opening of levees might adversely impact tidewater goby and steelhead (only in the Pescadero North Marsh area as the Butano North Marsh was not considered a problem then).

DPR projects in 1993 and 1997 included building or breaching levees and excavating channels to move sediments, improve tidal circulation and/or maintain fresh water areas. The results of the work, which included excavation of wide channels, the result of the work has increased hydrologic function in many areas. However, the work has created some compromises in natural function through the retention of some levees and construction of the culverts acting as tidal gates. This last measure was intended to improve the habitat for wildlife species dependent on fresh water increase tidal prism and allow flushing of sediment from North Pond (DPR synopsis of work).  Unfortunately, the low levee was too low and has eroded (after being raised somewhat once) and the culverts were never operated to maintain the desired habitats, they are now inoperative.

The freshwater habitat is now quite saline and unsuitable for red-legged frogs as well as one of their predators, the San Francisco garter snake. Deepening of the Butano channel was not undertaken.  Studies in 1995-6 (Smith and Reis 1996) indicated problems with the low levee and with salinity of North Marsh. These problems were aggravated by severe salt intrusion in fall of 2000 and 2002.

• DPR conducted water sampling studies in several locations during 2003 and 2004 in an attempt to understand the conditions causing the fish kills. Sixteen sampling sites were spread around the marsh in 2003 but mostly located in canals and points peripheral to the main lagoon, Butano and Pescadero creeks. Thirty nine sites were sampled in 2004 and included the sites sampled during 2003 in addition to the main channels and lagoon. The design of the sampling plan without a hypothesis led to soft observations about the problem.

• Fish kill locations were mapped beginning in 2003 and repeated in 2004 (as well as later years). Dead fish in 2003 were generally distributed along the southern shoreline from the pedestrian bridge (site WL) on the lagoon side and toward the highway bridge. Kill locations mapped in 2004 included this same area but also noted carcasses on the northern shore of Butano creek and the shoreline of Pescadero creek. A few fish were noted in the North Butano Marsh channel as well.

Field observations following the 2004 die-off included significant turbid water (black in color) in the lagoon and main channels at low tide. Fish carcasses were not noticed until the low tide following the breach. Dead fish were located along the perimeter of the water and extending only a limited distance into the vegetation. Significant populations of gulls and other birds were removing smaller carcasses. Steelhead trout casualties were of various sizes but were not emaciated and had good color except for indication of skin darkening (indicating shock) on a couple of fish. Examination of gill structure indicated particulate fouling and stomach dissection indicated active feeding behavior at the time of death (Steele). Dead fish were also noted washed onto the beach outside of the lagoon.