I think it depends a lot on the individual body of water, who controls it and what the demands are for that water. The lake I use is a reservoir owned by a water supplier who has a number of reservoirs in the Sierra Nevada foothills and mountains. I questioned the recreation department head of this water supplier and one of the lake operators and both told me that there was a strong commitment to keeping the launch ramps useable through at least the summer season.
I was concerned about this last year, also, but they kept the lake level plenty high all the way through to when I switched to snow skiing. I skied my first set on this lake last week and it was full to the brim. On the other hand, there are other NorCal lakes that are starting off lower than normal and became unusable last season, so, like I said, it depends on the individual body of water. Regardless, I am going to try to increase my set quantity in the early season because there are no guarantees as to when it will end.