Sources

Aldsay 1727 Avery Militairy map
Alltsay 1807 Arrowsmith
Altsay 1832 Thomson
Allt Saigh OS maps

Allt Saith Robertson 2019, 227
Allt-Saigh – the bitch burn – probably traceable to an ancient legend: c 1916, Gleannach, Glenurquart Field-names [manuscript notes by a local]
Allt Saigh x 2 Macdonald, A, ‘Scraps of Unpublished Poetry and Folklore from Lochness-side – No. II’ TGSI 23 (1898-1899) 179-208 [written in English text]
‘Craigsaigh, near Loudon House, is for creag saidhe, ‘bitch’s cairn ’ ; compare Alltsaigh in Glen Urquhart’ Watson 1926, 200
burn of the bitch: J. MacPherson, Glossary of some Place-Names, Inverness Field Club 1975