The fiord is relatively straight except near its mouth, when it turns northward, and has no major arms or indentations.

A straight ridge of peaks lies parallel with the fiord's south shore, between it and the valley of the Juno River.

The most favoured of these possibilities is that it was named for Jim Caswell, a half-caste Māori or Australian Aborigine guide to an early 19th-century sealing party.

Confusing things further is the presence of two other naval officers with the surname Caswell (George and Thomas) who had visited the area.

[2] In October 2019, the name of the fiord was officially altered to Taitetimu / Caswell Sound.