Storm clouds hovered overhead for most of the afternoon, but that didn't stop revellers enjoying the sounds of acts like Angus and Julia Stone, Peking Duk, The Wombats and Hayden James.

Headline act Childish Gambino pulled out of the festival due to injury, and while the news disappointed many, attendees were still enthusiastic.

Daniel Mallett made the trip to the festival from Melbourne.

"It was a little disappointing that Childish Gambino pulled out, but the festival found some good artists to cover for him," he said.

A pill testing service was originally slated for the festival, but plans were quashed after land owners the National Capital Authority rejected the move despite the support of the ACT government and pill-testing advocates.

The Sunday Canberra Times witnessed multiple festival goers attempting to hide drugs inside their pants as they approached the entrance to the festival, with a heavy police presence nearby.

Car parks near the venue were strewn with small sealable bags, often used to store pills. One had pills still inside.

While pill testing wasn't going ahead at the festival, multiple revellers said the initiative was much needed at festivals like Spilt Milk.

"It would be a good idea to have it there. The amount of people who buy drugs for a festival is ridiculous," attendee Ashleigh Granfield said.

"Having the safety of it there would be good, so people who were taking it for the sake of taking it would know what's in there.

"We would most likely use pill testing if it was there. We've been to other festivals where we don't know if we were taking anything, but it would be nice know that pill testing was there."

Fellow festival goer Will Peterson agreed.

"People will take pills regardless, but if they're tested it can inform them whether they're going to take it or not."

ACT Policing said they would be out in force around Commonwealth Park for the event.

"Police will maintain a high-visibility presence, targeting antisocial behaviour as well as conducting drink and drug-driving testing," Superintendent Jason Kennedy said.

"We want every participant to enjoy their evening, and do so without putting themselves at risk by taking illicit drugs. Not only is it illegal, it's potentially deadly."

Traffic along Commonwealth Avenue is expected to be congested this evening as the festival wraps up about 11pm.