Sources

Loch Awe is in Gaelic Loch Obha.: MacKinnon 1881
Loch O(bh)a; Loch (h)-O(bh)a
loX Xo’ə : Diack MS2276
L. Obha: Dieckhoff
Loch Odha: Bràiste Lathurna, 37
Loch Awe, Loch Obha.: Watson 1926, 75
Loch Awe is Loch Otha: undated newspaper clipping in CW collection
Loch Abh: Armstrong’s Gaelic Dictionary

The form for the Loch on the one hand and the river and inver on the other, are different:

Abha (’Atha’) (River) and Bun-abha, but Loch obha: Robertson

the river here is the Awe, Abhainn Abha (pronounced A’a), from Loch Awe, Loch Obha. What is the reason for the difference in vowel I cannot say, but it appears in other instances of abh.: Watson 1926, 75

In Argyll there is Abhainn Abha, the river Awe, with Bun Abha, Bonawe, ‘ Awe-foot ’ ; but Loch Awe is Loch Obha: Watson 1926, 477

Awe is Atha, but Loch Awe is Loch Otha . How is this? It was noticed the farther west you go the more prone a is to become o. Thus in Islay athainn (abhainn) is othainn, in Erin Calum is Colum, Lachlan is Loghlin: undated newspaper clipping in CW collection.

Additional Information

Forest Drive Loch Awe ~ Slighe-choille Loch-Obha

Alternative Forms