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Acreage/Location
The North/Estrada Marsh Complex is located on eastern side of Elkhorn Slough, approximately 3.5 miles from the mouth. This marsh complex is separated from the main system by a railroad embankment and tide gates. North Marsh, approximately 127 acres, is dominated by a mix of open water, mudflat, and fringing salt marsh habitat that is currently managed with a muted tidal range through the use of tide gates. Estrada Marsh, approximately 50 acres, is covered mostly with pickleweed (Salicornia virginica) and open mud pannes.
  
Past Human Activities (Modifications/Restoration/Management)
In 1869, Elkhorn Road was constructed on the east side of North/Estrada Marsh Complex, and it, at least minimally, reduced tidal exchange into Campagna and Strawberry Marshes.
  
A railroad, built in 1872 along the west side of North/Estrada Marsh Complex, blocked three of the four tidal creek connections (one to Estrada Marsh, three to North Marsh) with the main channel of Elkhorn Slough. The remaining tidal creek opening was under a railroad bridge with an open trestle.
 
In 1902, the Empire Gun Club purchased the land of the North/Estrada Marsh Complex. By 1913, this group created a number of large, artificial freshwater ponds (converted from tidal marsh) in the North/Estrada Marsh Complex using earthen dams to enclose areas and pipes to convey water from freshwater springs for the purpose of encouraging waterfowl prized for hunting. Between 1913 and 1931, landowners removed the southern half of North Marsh from tidal exchange by enclosing it with large levees so it could be drained. A levee was built separating Estrada Marsh from North Marsh between 1937 and 1949. By 1956, the entire North/Estrada Marsh Complex (including North and South Strawberry and Campagna Marshes) was removed from tidal exchange by a series of levees. One of these levees (with a horseshoe-shape) blocked off the remaining large tidal creek connection from the main Elkhorn Slough system. This levee may have contained a water control structure such as a flap gate that allowed freshwater to enter Elkhorn Slough during flood events, but did not allow tidal waters to enter this area. The draining of the tidal marsh areas during this time caused the marsh sediments to dry out, compact, decompose, and subside by, on average, 2.3 feet (0.77 meters).
  
The California Department of Fish and Game acquired North Marsh in 1980 and Estrada Marsh in 1993 as part of the Elkhorn Slough National Estuarine Research Reserve. Soon after the Reserve was designated, CDFG managers began discussing the possibility of restoring tidal flow to 125-acres of reclaimed North Marsh lands to enhance habitat by excavating tidal creeks, creating habitat islands, and grading to add topographic features. The plan was to have the maximum tidal inundation possible without flooding Elkhorn Road to the east by adding tide gates to the previously blocked culverts in the horseshoe-shaped levee by the railroad bridge. During major storms in December of 1982, the horseshoe-shaped levee failed causing Elkhorn Road to flood. Monterey County then raised the road in 1985 to mitigate the effects of flooding. That same year, contractors were hired to replace the failing water control structures. Once this work was completed, tidal action was returned in the summer of 1986, through four new tide gates.
Like many structures used in marsh management, the North Marsh levee and tide gates have required a great deal of maintenance, repair, and continued, intensive management over the years. Repairs have included the rebuilding of the main levee after a washout in the early 1990s; the replacement of several rusted tide gate stems; and repair to gate hinges. Maintenance has included the annual placement of several tons of sandbags on top of the levee to prevent overtopping by extreme high tides; the building up of levee elevation using dirt and large riprap; annual cleaning of gate flaps and removal of fallen riprap by SCUBA divers; and monthly maintenance of all tide gate stems. Ongoing management involves the opening and closing of tide gates to adjust water levels.
  
The earthen levee separating North Marsh and Estrada Marsh partially eroded in the summer of 2003, resulting in a narrow creek (approximately 1 m wide) between the two wetlands. This creek has restored a minimal amount of tidal flow to Estrada, but it is currently too small to allow for true tidal exchange. Currently, tidal flow enters Estrada, but does not appear to drain. Instead, ponded tidal water evaporates over the summer months, resulting in seasonally hypersaline conditions throughout much of the Estrada marsh.
Current Management/Ownership
North Marsh is owned and managed by the California Department of Fish and Game as part of the Elkhorn Slough National Estuarine Research Reserve which is administered by NOAA. Estrada Marsh is also owned and managed by the California Department of Fish and Game, but is not part of the Reserve system.
 
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