The Arcata Marsh & Wildlife Sanctuary is a wetlands preserve that circulates effluent from the Arcata wastewater treatment plant. It covers 307 acres on the edge of Humboldt Bay, with 225 acres accessible to the public through a network of trails. The Sanctuary consists of freshwater ponds, a salt marsh, a brackish water pond, tidal mudflats, and an interpretive center. It is managed by the City of Arcata
The Marsh once was the site of a landfill and several lumber mills. Today, "Mount Trashmore" sits on the landfill site and supports grasslands and pine trees that attract many wildlife species. The former leach pond is now a brackish water pond known as Klopp Lake, where thousands of shorebirds visit annually. The interpretive center sits on the foundation of a defunct mill and is home to wildlife art displays, interactive exhibits, and a book and gift shop.
The wastewater treatment plant handles all sewage for the City of Arcata. Raw sewage enters the headworks, where the sludge is separated from the effluent. The sludge is digested, dried, and composted for use on city grounds. The clarified wastewater is sent to the 49 acres of oxidation ponds where time, aquatic plants, and microorganisms purify it. Arcata's wastewater then circulates through a six-marsh system, filled with plants and animals that feed on the nutrients that are left. The water that is finally discharged into Humboldt Bay has gone through "enhanced" secondary treatment, thanks to the marsh system, and is completely potable.
Wildlife abounds at the Arcata Marsh. Since it is located on the Pacific Flyway, the Marsh is permanent and temporary home to over 300 species of birds. The trail system includes over 4.5 miles of walking and biking paths that meander through the wetlands, beside the bay, and around the oxidation ponds. The beautiful scenery and abundant wildlife make the Marsh a perfect place to walk, jog, take photographs, and relax. Dogs must be leashed at all times.
Visitation at the Interpretive Center continues to grow each year, reaching 21,105 walk-in visitors in 2009/10. This represents a tripling since 1995.