Lost Slough is a tidal slough within the Cosumnes River Preserve in California's Central Valley, forming part of the Sacramento-San Joaquin Delta system. It is characterized by a maze of quiet, narrow channels winding through restored marshes and riparian forests, creating a peaceful and isolated paddling environment where it is easy to become disoriented. A primary access point for a one-way trip is the concrete launch ramp at the former Delta Meadows State Park near Locke; this ramp is steep and slippery, with limited access requiring wheels to transport boats and no facilities available. An alternative entry for experienced paddlers seeking a shorter route into Lost Slough is via a "back door" channel accessible from the Cosumnes River Preserve Visitor Center area, which involves paddling under the Franklin Boulevard bridge; this route can feature very shallow water and require portages over sandstone during low tides. The destination for a common shuttle trip is the Cosumnes River Preserve, creating a popular one-way route of approximately 10 to 16 miles when combined with connecting sloughs like Snodgrass Slough and the Mokelumne River.

Paddling here is heavily influenced by tides, as the slough connects to the tidal Delta. Tides can be extreme, with very low water levels occasionally necessitating portages where paddlers must carry their boats over hard, flat sandstone. The area experiences minimal powerboat traffic, with only a couple of fishing boats encountered on typical journeys. There are no significant surf zones or high-wind fetch concerns within the protected slough channels, but paddlers must be prepared for navigation challenges due to the many intersecting waterways. The scenery includes lush marshes, valley oak riparian forests, cottonwood/willow stands, and tule marshes, with wildlife including numerous bird species. Historical remnants like an abandoned boat and old bridge footings can be seen. The Lost Slough Wetlands Boardwalk, part of the preserve's trail system, offers a land-based view of the area but is separate from the paddling route. The preserve is open from sunrise to sunset.