Not just SP's close proximity, but local RSOs proximity as well, IMO.
I was actually just discussing this with my mother-in-law earlier, but assuming that you haven't been to Shasta Lake, it is very murky and hard to see anything that goes about 1 foot into the water. I have gone there many times to swim over the summer and it always seems like its pretty murky. Searching it would be very difficult due to the large size and vast amount of areas around it but that's not to say it shouldn't be done. Considering her close proximity to the lake, I too have wondered why there is no mention of searching it, unless they believe it to be fruitless.