Loch Arienas is an extensive, lowland, freshwater loch on the Ardtornish Estate on the Morvern peninsula in the Scottish Highlands. It lies in a west-northwest to east-southeast direction, is approximately 3.2 km (2.0 mi) long and 1.21 km (0.75 mi) wide, and is at an altitude of 12 m (39 ft). The northern shore of the loch is mostly regular in shape, while the southern shore is irregular. Its average depth is 17.2 m (56 ft) and its maximum depth is 35 m (115 ft). The loch was surveyed on the 18 and 19 of August 1904 by John Hewitt as part of Sir John Murray's Bathymetrical Survey of Fresh-Water Lochs of Scotland 1897-1909.