No new law has been passed. The person at the helm can get a BUI; everyone else, whether at the putin, takeout, or on the river, can get an open container and/or public intoxication ticket- the river is a public place- so the old laws apply.
The reason they are trying to enforce it more now is because they considered making a new city ordinance, but understood that it would be unenforceable so they are going to try to enforce the laws already in place.
What really sucks about it is that the city ordinance was originally designed to require PFDs on the river and somehow that turned into a ban on booze and a curfew for floating- none of which has been passed.
A ticket will be given for liquor as well as beer, but having a Nalgene full of "something" is not probable cause I don't think- flying the blue ribbon is.
"There is NOTHING--absolute nothing--half so much worth doing as simply messing about in boats. Look here! If you've really nothing else on hand this morning, supposing we drop down the river together, and have a long day of it?" -Wind in the Willows