Are passengers on a boat allowed to drink alcohol?

I've never heard of a law that says passengers can't drink, as long as alcohol is legal where it is being consumed.
In Florida state parks, and some county parks and recreation areas, acohol is banned, period. If caught you face possible fines and jail time, especially if intoxicated. Mostly the cops will search your coolers and make you empty any acoholic beverages found.

As Iggy indicated; The rules vary depending on where you are, what state in the US, or what province in Canada. Some places forbid any consumption while underway, some only restrict the driver. Best check you local laws. --- Jer

In the states I have boated in, both passengers and the driver can drink alcohol. The driver just can't be over the legal limit.

Up here, no one can drink on any boat under way period. Only once a boat is docked, anchored or moored is it considered a "residence" and only if it has cooking, sleeping and head facilities is it legal to consume alcoholic bevies then. The water coppers have a nasty trick for nailing illegal drinkers. They cruise around in a small, unmarked boat at the local hangouts with one of those parabolic mikes listening to conversations. Then a marked cop boat cruises in and they nail the folks who say "quick, hide the beer" !

I thought drinking was legal when parked?

It's the Law: On the Water With Your Boat or PWC
Alcohol and Drugs
Virginia law states that a person is considered to be “under the influence” if:

He or she is 21 years of age or older and has a blood alcohol concentration of 0.08% or higher, or is under the influence of alcohol and/or drugs to a degree which impairs his or her ability to operate safely.
He or she is under 21 years of age and has any measurable blood alcohol concentration (0.02% or higher), or is under the influence of alcohol and/or drugs to a degree which impairs his or her ability to operate safely.
Virginia law establishes the following penalties:

Those convicted of operating under the influence of alcohol or drugs will:
Receive a fine of up to $2,500
Be imprisoned for up to 12 months
Lose the privilege to operate a boat for up to three years
Be required to attend an Alcohol Safety Action Program.
By operating a boat or PWC on Virginia waters, you have consented to be tested for the presence of alcohol, drugs or other intoxicating substances if requested by a peace officer. Any person refusing to submit to testing for the presence of alcohol, drugs or other intoxicating substances may lose his or her privilege to operate a boat for up to 24 months

Post #7 is all dept. of game and fish has for laws on line on alcohol and boating, they don't want to tell you that you can drink or not.

Wo Wo ...i know for Ontario ....but here on the french side we have the right to drink alcohol..... The driver just can't be over the legal limit ....like you know we alway's do someting different of you ......but you have so beautiful place for boating .....i dream to get back to Georgian Bay .....
Best Regard's

There's an understatement.