DENVER — Thousands are expected to gather at Denver’s Civic Center Park Saturday for the 4/20 rally.

The event, which takes place every year on April 20, is expected to draw an even larger crowd since Colorado passed Amendment 64 this year. Even though the amendment makes it legal to possess up to an ounce of marijuana for those 21 and over, police are emphasizing that it is still illegal to smoke pot in public.

Organizers say they are expecting 80,000 people to show up this year, compared to last year’s crowd of 50,000.

This is also the first year that Denver will celebrate the Cannabis Cup, a marijuana-themed convention where pot growers get the chance to compete for things like best taste, appearance and potency of their marijuana. The Cannabis Cup is normally held in Amsterdam.

Earlier in the day, the University of Colorado Boulder announced that the campus was closed to the public in order to avoid 4/20 disruptions. Only students, university employees and approved campus affiliates were allowed on campus. CU Boulder used to be home to April 20th’s largest smoke out.

There was also increased police activity both in Denver and Boulder.

Denver’s 4/20 rally is free and open to the public, and will run from 9 a.m. to 6 p.m. Saturday, and from 9 a.m. to 5 p.m. Sunday.