Uh-oh alien invader?

Uh-oh alien invader?

Observation - Uh-oh alien invader? - Southern Africa. Description: Great swaths of small, elongate, conically-shelled snails on damp sandbar and underwater in adjacent

Great swaths of small, elongate, conically-shelled snails on damp sandbar and underwater in adjacent stream. Risked stepping on them.
The stream is tidal nearer the mouth, but at this point some half-a-kilometre from the beach, freshwater.
Varied in length from about 10 - 18mm (the largest, darkest, close-up shown).
Heavily tubercled shell, coiling to the right.
Doesn't look like indigenous Red-rimmed Melania ( Melanoides tuberculata) to my eye though Tarebia is (was?) supposedly confined to northern KZN ...