Tens of thousands of people descended on a waterfront park in Seattle on Friday for the opening of what's billed as largest marijuana rally in the United States.

The event has a pressing political edge this year: Washington state voters will consider an initiative that would legalize the fun use of pot for adults. Colorado, Oregon and Washington already have medical marijuana laws, and all three have legalization measures on the November ballot.

Washington's would allow sales of up to 28 grams of dried marijuana at state-licensed stores and could bring the state nearly $2 billion US in tax revenue over the next five years — if the federal government doesn't try to block the law from taking effect. Pot remains illegal under federal law.

Initiative 502, also would prevent nearly 10,000 marijuana possession arrests every year in the state, proponents say.

"It looks like we're finally reaching a critical mass to end this critical mess," Hempfest director Vivian McPeak said as the festival began. "If I-502 passes, it'll be a historic moment."

Organizers expected at least 150,000 people at the three-day event. Thousands milled along the 1.5-mile long park under a blazing sun Friday afternoon, stopping at booths advertising colorful glass pipes, hemp clothing and medical marijuana dispensaries. Young women shouted at passersby to encourage them to obtain medical marijuana authorizations — "Are you legal yet?" — while other festival goers rested on driftwood logs, lighting joints and pipes.

Vendors hawked $2 bottles of water, but not just for hydration: "Ice water here! Get some ice water for your bong!"

Despite the pot-tolerant crowd, there was no consensus as to whether I-502 is the right thing for Washington's marijuana smokers. The measure has garnered opposition from the medical cannabis community, and some say its driving-under-the-influence provisions are so strict that it could prevent them from driving at all.

'It looks like we're finally reaching a critical mass to end this critical mess.'— Hempfest director Vivian McPeak

Others say the measure doesn't go far enough because it wouldn't allow people to grow their own pot for recreational use, although medical patients still could; it doesn't contemplate the industrial growing of hemp; and it would not allow recreational use for those between 18 and 21.

Because of the split, Hempfest — now in its 21st year of advocating legalization — is taking no official position on the measure, something McPeak called "very painful and very awkward."

Alison Holcomb, campaign manager for the measure's sponsor, New Approach Washington, said she was disappointed, too.

"We've got a legalization measure on the ballot right now," Holcomb said. "Seattle Hempfest, which has been carrying the legalization banner for 21 years, ought to be celebrating."

Both sides of the debate were aired at the festival, as supporters and opponents set up tents and vied for the attention of potential voters.

At the No on I-502 tent, activist Arthur West said he's been attending Hempfest since the late 1990s and never imagined that he'd be here to oppose a legalization measure. However he and fellow activist Poppy Sidhu said they don't consider I-502 legalization at all.

"We're all for legalization, but legalization, for me, is being able to grow as much as I want and being able to walk down the street to Starbucks smoking my joint," Sidhu said.

Conner Michaels, 24, of Bellingham, approached with a thick, burning blunt in his hand and asked for a No on I-502 button.

"This is sick," he said. "I'm not going to be able to drive if this passes."

Dispensaries oppose measure

Medical marijuana dispensaries are largely also opposed, in part, because of the licensing requirements in the measure, said Brian Ray, the goateed, dreadlocked owner of One Love Collective, a dispensary in South Seattle. Many dispensaries are doing well under the current system, and there's no reason to rush into a legalization scheme that might be flawed, he said.

"It appears like it's going to shut down the entrepreneurial spirit of these small businesses," Ray said.

Breast cancer survivor Cindy Denny, 52, and her husband, Kerry Denny, had a different view as they surveyed the largely younger crowd. She said that she is still taking oral chemotherapy, and the marijuana helps her feel better. But when she first tried to obtain an authorization as required by state law, her chemo doctor wouldn't give her one because it remains illegal under federal law.

She said she had to go to a different clinic to find a doctor who would write her an authorization, and that hurdle might be too much for some patients.

"It's not working the way it is right now," added Kerry Denny, a retired Teamster. "You can regulate it and tax it like everything else."