[1][2] Fallowlees Flush is situated in the north-east of England in the county of Northumberland, to the west of Fontburn Reservoir and the east of Harwood Forest, 7.8 kilometres (4.8 mi) west-north-west of Netherwitton and 4.5 kilometres (2.8 mi) east-south-east of Forestburn Gate.

[1][2] Flora on the site grades from species rich areas fed by lime-rich springs, through to a wooded fringe by the stream.

[2] A wider area is influenced by the springs, and in addition to the sedges and cottongrass, supports dioecious sedge (Carex dioica), marsh lousewort (Pedicularis palustris), creeping willow (Salix repens), devil's-bit scabious (Succisa pratensis), purple moor-grass (Molinia caerulea), marsh cinquefoil (Potentilla palustris), meadowsweet (Filipendula ulmaria), jointed rush (Juncus articulatus) as well as common butterwort (Pinguicula vulgaris), grass-of-Parnassus (Parnassia palustris), marsh valerian (Valeriana dioica), and early marsh-orchid (Dactylorhiza incarnata).

[2] Woodland areas by the stream are composed of alder (Alnus glutinosa), downy birch (Betula pubescens) and hazel (Corylus avellana).

Ground flora in the woodland area includes tufted hair-grass (Deschampsia cespitosa), water avens (Geum rivale), wood crane’s-bill (Geranium sylvaticum) and a substantial stand of lesser pond-sedge (Carex acutiformis).