The use of alcohol on river rafting trips varies around the country and internationally. It has always been a debate as to whether alcohol should be allowed, if so, can customers bring their own, should it be limited to........ and so on.
The American River in California has seen a large impact with restrictions on alcohol use one the river. Right now, the government prohibits alcohol use on any river on holidays and holiday weekends. One report quoted an outfitter saying that because of the ban, the river is much quieter and more peaceful. The Fourth of July this year did not turn out so many fights and problems, which can be directly correlated to alcohol consumption on the river.
So with one successful story of how bans on alcohol have affected river patron, what other locations can follow suite? Larger rafting outfitters (Grand Canyon, Idaho, Glacier Park) with longer multi-day vacations allow guests to bring their own booze, but it is limited and controlled to a certain point (hopefully). But smaller operations and daily rental places may not have the control over what customers bring on the river.
Either way, I think it is still in every one's best interest to limit/prohibit alcohol consumption on the river.