Historic Resource Study, Crater Lake National Park, Oregon, 1984
V. Geological and Biological Information on Crater Lake Area
G. Will Mount Mazama Erupt Again?
No volcanic activity has been observed recently at Crater Lake, but there have been scares. On September 15, 1945, a fire spotter on The Watchman saw what she later described as a strange cloud of smoke or fog rising sharply from the lake’s surface in a compact mass before mushrooming into a larger diameter. Two days later a similar cloud was spied from Garfield Peak’s summit on the south side of the rim. A third was seen from a viewpoint near the Devils Backbone between Hillman Peak and Llao Rock on the northwest side of the lake. Each of these vapor “clouds” was described variously as being dust-colored or of a bluish-gray hue, each was seen on a clear day, and each was spotted at approximately the same location, over one of the deepest portions of the lake on an east-west line between Wizard Island and the Phantom Ship. 
Although no earthquakes that might presage volcanic activity had been reported, speculation immediately arose that the dormant volcano might blow its top again. Such alarm might not have arisen if there had not been in years past instances suggestive of continuing volcanic activity in this area of the Cascades. As early as 1896 J.S. Diller was stating that “the increase of temperature [in the lake] with the depth suggests that the bottom may yet be warm from volcanic heat. . .” A 1919 Oregonian (Portland) article noted an eruption in Diamond Lake that killed thousands of fish and discolored the waters. A month later an “underwater disturbance” in a lake near Albany, Oregon, was remarked upon, “similar to that reported in Crater and Klamath lakes.” 
Despite reassurances from Dr. Howel Williams that “once collapse occurs there is little chance of violent activity in a caldera, although occasional periods of minor activity may occur for an indefinite period,”  the Department of the Interior promised to send members of the Geological Survey to study the phenomenon. Both local and national interest were manifested in the supposed “eruptions,” with a story appearing in Time magazine for November 12, 1945, and similar ones being disseminated by the Associated Press, the United Press, and the International News Service.
The government study involved planting a sounding device, a Navy hydrophone, in the lake, which operated well until a heavy January snowfall caused a landslide that snapped the cable connecting the device with the recording instruments sequestered in an observation station in Crater Lake Lodge. The cable was carried out into the lake, leaving the study unfinished and the hydrophone stranded inoperable in the water for the duration of the winter. Up to that point, however, no evidence of volcanic activity had been noted, and with the cessation of further “cloud” sightings, this potential threat from Mount Mazama seems to have had no further developments.