This site is located where the Chehalis River empties into the lower Harrison River, just upstream from its junction with the Fraser River. The town of Harrison Mills is nearby, and Chilliwack is about 10 kilometres to the south. The Chehalis River enters the Harrison River in a broad fan of meandering channels and mudflats. Sedge marshes cover much of the open habitat at the mouth of the Chehalis River, while the Harrison River is bordered by linear stands of large Black Cottonwood, Western Redcedar and Douglas-fir. The site is within the lower Fraser Valley, a broad floodplain (~15 km wide) bordered on the north by the granitic Coast Mountains and on the south by the Cascade Mountains. Coho and Chum Salmon have a winter spawning run here.

This area attracts large numbers of Bald Eagles from December through February, which feed on spawning Coho and Chum Salmon. Exact peak numbers are difficult to obtain, but 400 to 500 are regularly seen from the Harrison Mills bridge on Highway 7 in mid-January, and the area total is generally around 1,000 birds at that time (1% of the global population). The total on the Christmas Bird Count in this area in December, 1997, was 1,235 birds. This eagle concentration is globally significant and is perhaps the third largest in the world after the Chilkat River, Alaska, and Squamish River, British Columbia.

Trumpeter Swans of the Pacific population are also present in globally significant numbers, with 413 being seen in the area during the 1997 Christmas Bird Count. This represents 2% of the worlds population of this species. Numerous other waterfowl species use the area in winter also.

Tree-cutting for housing developments reduces the number of roost trees available for the eagles. Also, Eagle concentrations are highly dependent on salmon populations, which have been generally declining on the Pacific Coast due to over-harvesting, habitat degradation of spawning areas, and other factors.

This area is easily accessible along Highway 7, and the concentration of eagles is an important wildlife viewing opportunity for residents of the Lower Mainland, including Vancouver. Some of the land in the area is controlled by the Nature Trust of British Columbia.