Fisher Island Slough is a tidal waterway on the Columbia River in Cowlitz County, Washington, separating Fisher Island from the mainland. The primary and only identified public access point is the Willow Grove Park boat launch in Longview, which offers a concrete ramp, ample parking, and no launch fee. The slough itself is a narrow, meandering channel characterized by calm, shallow waters and a backdrop of wetlands, making it a suitable environment for beginner kayakers and stand-up paddleboarders. Its protected nature limits wind exposure and wave action. However, paddlers must be acutely aware of the significant tidal currents in this area. A trip report from a sea kayaking group details paddling against a "significant current" in the slough, and planning must account for the Columbia River's substantial tidal exchange, with one organized trip noting a high tide of 5.2 feet and a low tide of 0.3 feet on the same day. Currents in the vicinity can reach 2 knots.

Exiting the slough onto the main Columbia River presents a different set of challenges. The river is a major shipping corridor with commercial vessel traffic, and paddlers may need to make open-water crossings of up to a mile to visit other islands like Walker and Lord. These crossings require appropriate skill and situational awareness. A common day trip is a circumnavigation of nearby Crims Island, which involves two Columbia River crossings and covers approximately 10 to 12 nautical miles. The water is cold year-round, with estimated winter temperatures around 38 degrees Fahrenheit, necessitating proper immersion protection such as a drysuit. Motorboat traffic within the slough is regulated by a mandatory slow-no-wake speed zone for its entire length, which helps maintain calm conditions. Wildlife sightings are a highlight, with frequent observations of sea lions, swans, and a variety of birdlife in the surrounding lagoons and channels.