The river rises at various sources near Earlswood Lakes, but the principal tributary is listed as Spring Brook[1] (52°21′03″N 1°50′37″W / 52.350915°N 1.843601°W / 52.350915; -1.843601; grid reference SP107725).

At Temple Balsall the Cuttle Brook feeds the river, which now arcs north, and again close by Barston.

[2] The Blythe has a wide range of natural geographical features such as riffles, pools, small cliffs and meanders, combined with a high diversity of substrate types ranging from fine silt and clay in the lower reaches to sands and gravels in the upper and middle reaches.

[2] However, physical modification to the watercourse and the riparian zone has impacted the functionality of the River Blythe, resulting in the SSSI's condition labelled as "unfavourable no change" in 2017.

[1] The factors leading to this were mainly due to historic management; many sections of the river have been straightened, and the riparian zone modified and disrupted, upsetting the site's ecological health and lowering the overall SSSI status.