VANCOUVER -- The Vancouver Parks Board says it has to close a popular park because of damage caused during an annual cannabis celebration, but pot advocates are disputing the blame.

Parks Board chairman Stuart Mackinnon says staff will need about 10 weeks to repair the damage to Sunset Beach Park, which hosted about 40,000 people at the 4-20 celebration on Friday.

He says although organizers made efforts to reduce damage this year, including laying field-protection panels to shield it from rain, it wasn't enough.

Mackinnon says staff will have to wait for the field to dry completely before aerating, top-dressing, seeding and fertilizing it -- then letting the grass re-grow.

Cannabis activist Jodie Emery characterized the finger-pointing as smear messaging against the marijuana movement, posting photos on Twitter comparing the field before and after the event.

She described the field afterward as "green and grassy," with the same mud puddles that existed before.

"On April 14, I took photos and video and found many water puddles from the rain and muddy sections. But with our $30,000 of covering and responsible organization and the promise to re-seed if it's needed, the grass at Sunset Beach today looks better than before," Emery said in a phone interview with The Canadian Press.

She said organizers have worked hard to address all criticisms from past events, including renting the concert-grade turf covers and carding participants to keep out minors.