Both these years Emerald Bay froze over.

Perhaps the reason for this is found in the fact that the entrance to the bay is very shallow, and that this meager depth is subject to change in surface temperature, becoming warmer in summer and colder in winter.

This narrow ridge once solidly frozen, the warmth of the larger body of water would have no effect upon the now-confined smaller body of Emerald Bay.

Once a firm hold taken by the ice, it would slowly spread its fingers and aid in the reduction of the temperature beyond, first producing slush-ice, and then the more solid crystal ice, until the whole surface would be frozen solid.
An explanation of the non-freezing of the main Lake has been offered by several local "authorities" as owing to the presence of a number of hot springs either in the bed of the Lake or near enough to its shores materially to affect its temperature.

But I know of few or no "facts" to justify such an explanation.
When I first visited Lake Tahoe over thirty years ago I was seriously and solemnly informed by several (who evidently believed their own assertions) that, owing to the great elevation of the Lake, the density of the water, etc., etc., it was impossible for any one to swim in Lake Tahoe.