The threshold for mortality in S. salar is about 23°C (Shepard 1995), although according to some other authors it could exceed 27°C, and even be as high as 29 to 30°C (Mills 1989). This value is mainly dependent on the acclimation of the fish and the duration of exposure (Shepard 1995). In salmonids, the direct effects of elevated temperatures are associated with increased metabolic demands that exhaust their energy reserves (Glebe & Leggett 1981), and may be exacerbated by other factors, including reduced disease resistance and increased susceptibility to disease (Cairns et al. 2005). Temperatures in the range of 20 to 27°C reduce resistance to disease, and thus may be indirectly lethal for S. salar (Danie et al. 1984).
27°C = 81° F
Any form of reservoir certainly isn't helping as it allows the water to heat up faster. Chances do seem slim that the Credit, Bronte, Humber will be able to provide the summer temps and oxygen content necessary for Atlantics to be able to support successful spawning runs. But it'd be amazing if a new Lake O strain developed out of this project. I get the feeling that the majority of the nay-sayers are just being political. I haven't seen a lot of well researched numbers showing why the program won't possibly work.