The McNary Lock and Dam on the Columbia River created a 62-mile long, 37,000 acre reservoir (Lake Wallula) with 242 miles of shoreline and its associated 16,908 acres of Corps-owned shorelands managed under the McNary Dam Project. Some of the lands have been extensively developed and used for various public purposes, principally port, industry, and recreation, and other areas are managed for wildlife.
In the 1970s, the Corps created three islands in the Columbia River composed of rock materials excavated from the Snake River channel below Ice Harbor Dam. These islands have been termed Upper, Middle and Lower Shot-rock Islands, and are 9, 10, and 12 acres in size respectively. Attempts have been made to add topsoil and plantings to the three islands to provide habitat for terrestrial species, primarily waterfowl and other birds. In the 1980s, habitat enhancement efforts on the Upper Shot-rock Island were not successful. Failure of the plantings was likely due to the height of the upper island above the river level, which made the water table inaccessible to most planted vegetation. Upper Shot-rock Island is sparsely vegetated, and provides limited habitat value. The riparian zone coverage is sparse, largely due to the rocky substrate and the steep sides of the island as it is now configured. Later enhancements at the middle and lower islands included lowering the islands’ profiles with respect to the river and adding finer-grained material for planting. These efforts have had greater success.
In August 2003, the Walla Walla District U.S. Army Corps of Engineers (Corps) under the authority of Project Modifications for Improvement of the Environment, Section 1135 of the Water Resource Development Act of 1986 (PL 99-662), completed a Preliminary Restoration Plan (PRP) for the Two Rivers Park, Benton County Washington. The PRP determined that there is enough federal interest to warrant the initiation of a feasibility study for ecosystem restoration of Upper Shot-rock Island.
Two Rivers Park is a day-use park owned by the Corps and leased by the Benton County Department of Parks and Recreation. The park is located on the right bank of the Columbia River, directly across from the mouth of the Snake River at river mile 324. Much of the natural shoreline along the section of the Columbia River above and below the park was replaced with levees associated with construction of McNary Dam. However, Two Rivers Park retained much of its natural shoreline which includes river interface with a large wetland system.