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Lower reach of Arroyo Corte Madera del Presidio immediately after tidal efflux to Richardson Bay.

Arroyo Corte Madera del Presidio is an intermittent stream in southern Marin County, California, USA. This watercourse has a catchment basin approximating six square miles and drains the eastern slopes of Mount Tamalpais and much of the area in and around the town of Mill Valley; this stream discharges to Richardson Bay.

A 1965 stream survey indicated presence of steelhead within 100 feet of the dam. A 1990 study indicated the water quality of upper Richardson Bay below the discharge of Arroyo Corte Madera del Presidio to be impaired by high nutrient and coliform levels;^[1] This same study indicated that Arroyo Corte Madera del Presidio is subject to periodic flooding.

A private organization, the Mill Valley Streamkeepers, is active in research and conservation of this creek.

Arroyo Corte Madera del Presidio non-tidal lower reach through residential area of Mill Valley.

The first recorded stream survey occurred in the year 1946; this survey by the California Department of Fish and Game found some healthy Oncorhynchus mykiss within the stream.^[2] The next Department of Fish and Game survey transpired in 1963, finding numerous steelhead of lengths varying between five and fifteen centimeters; this survey concluded that the lower 3.5 miles of the creek represented an important nursery and rearing habitat for steelhead and possibly for Coho salmon. The next survey in August 1965 concluded that the habitat was an excellent resource, with deep shaded pools and an average of 75 steelhead per 30 meters of lineal stream. In 1984, steelhead were still found to be present. A 1991 stream survey documented the historical presence of Coho salmon.^[3] The next survey in 1994 found abundant steelhead, ranging from densities of 0.1 to 0.7 fish per square meter.^[2] The 1997 stream survey found densities of steelhead ranging from seven to twelve fish per 30 lineal meters, depending on stream reach.

The stream's discharge location, into Richardson Bay occurs within the Mill Valley municipal Bayfront Park. The Arroyo Corte Madera del Presidio enters Richardson Bay from the west, while Mill Creek enters Richardson Bay nearby from the north via Bothin Marsh. Bayfront Park features many active uses including a bicycle path, walking paths, a dog park and picnic areas. The park also features a pedestrian/bicycle bridge across the tidal portion of Arroyo Corte Madera del Presidio, which is the best single viewing location of the creek in its lower reaches. Slightly further upstream the stream winds through moderately dense single family development, with backyards offering terraces and decks on the banks of Arroyo Corte Madera del Presidio.

The Mill Valley Streamkeepers is a private non-profit organization established to promote research, awareness and conservation of streams in the Mill Valley area. This group includes scientists and laymen and has participated in the following specific studies involving Arroyo Corte Madera del Presidio:^[4]

• Feasibility Study to Rehabilitate the Fishery Resources of Arroyo Corte Madera del Presidio
• Bio-assessment of four Marin County Watersheds
• Macroinvertebrate Sampling and Identification Study, Arroyo Corte Madera del Presidio and Old Mill Creek
• Salmonoid Habitat Survey and Erosion Survey, Arroyo Corte Madera del Presidio and Old Mill Creek

• Bay mud
• Richardson Bay

• California Coastal Salmon and Steelhead Stream Habitat Distribution Table: including data for Arroyo Corte Madera del Presidio

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