The river is a complex of spring-fed lakes and waterways originating in Ahjumawi Lava Springs State Park in north-eastern Shasta County in northern California.

[6] The lake complex and marshlands are an important stopover on the Pacific Flyway for Canada and snow geese as well as American white pelicans, and blue-winged teals.

Other bird species include Lewis's woodpeckers, northern pygmy owls, bald eagles and a large population of ospreys which nest in juniper trees, a situation unique to the area.

In addition sportfisherman angle for non-native largemouth black bass Micropterus salmoides, and brown bullheads (Ameiurus nebulosus).

PG&E proposes to donate McArthur Swamp and the nearby parcel acquired by a land trade with State Parks (see Lake Britton) to the Fall River Resource Conservation District, which is to manage it subject to a strict easement.