Thackthwaite is a 10.2 km² subcatchment drained by Thackthwaite Beck in the west of the Eden north of Ullswater, a tributary of Thackthwaite Beck which flows into the Eamont at Dalemain near Stainton. Thackthwaite Beck upstream of Skitwath Beck is classified as waterbody ID GB102076070890. The Thackthwaite catchment drains to an outlet at Nabend, between Great Mell Fell (537 m) and Little Mell Fell (505 m). Thackthwaite is the highest altitude of the DTC subcatchments. The area is dominated by improved grassland, over Siliceous (sandstone) bedrock.