I remember being told by Ray Elshire (who no longer works there) that they could launch houseboats down to a lake level of 3,555.
In recent photos of the Valet Ramp, you can tell that they "cleaned up" the end of the ramp where the cliff was dynamited during the original construction. They were not allowed to extend the concrete, but you can see where there is freshly exposed rock with no mussel build up. That work might have dropped the lowest launch level to 3,550 or maybe even 3,545, but that is just my guess.