Explorer David Thompson mentions the river in 1810: we crossed the the Pembinaw River of forty yards in width.1 This pronunciation is a European distortion of the Cree word “neepinmenan”, or summer berry.2
In this despatch from 1862, Douglas mentions a passage in Mackenzie's narrative of the overland Journey from Canada, which relates that a valuable seam of Coal crops out on the Pembina.
1. Tracey Harrison, The Place Names of Alberta, vol. 3, Central Alberta (Calgary: University of Calgary Press, 1994), 195.