If you read the old literature on how controversial it was at the time, those supporting the dam said it would increase the leisure use of the site, giving it a great lake to camp and fish at. They literally believed it would improve the natural surroundings.

Even modern say SF offices still use that line: "They were eager to show us how, they say, the reservoir actually enhanced the beauty of the valley,"

http://www.pbs.org/newshour/bb/environment-july-dec05-dam_8-...

I didn't say it was the motivation of the project, just that it has been claimed and used to buttress other arguments.