The popular city park was packed for most of the day, with many groups drinking and socialising in the sunshine.
Coronavirus rules were relaxed this week to allow groups of six to meet outside, but concerns have been raised at the number of people seen breaching the regulations.
This morning, the park is covered in litter, with empty beer bottles, cans and takeaway wrapping strewn across the grass.
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Bins are overflowing, with piles of rubbish stacked against them on the ground.
One shocked Endcliffe mum said: “It is awful this morning, I have never seen it this bad.
“The park was absolutely rammed yesterday and the roads were totally gridlocked.”
Photos of the huge crowds sparked outrage from some yesterday.
Craig Bell said the park had been ‘trashed with litter’.
Louise Meadows described the crowds as ‘absolutely disgusting behaviour’ and ‘selfish’.
Angela Milnes said: “On Rustlings Road when I drove home, cars were parked on double yellows. Couldn't see the grass for people at 4pm.”
Outraged Christine Donson said: “What is the society of Britain becoming.
“Over 126,000 people have died. Are they just numbers?
“I want some life back more than many as I have incurable advanced cancer and have wasted one year of it stuck inside watching others taking the p!
“Should I just add a number to the list so selfish childish people can enjoy themselves?
“Shame on those who have little thought for others and make cruel comments when some people are genuinely worrying. Dying is not a joke and when your time comes you might just stop and think of your actions. Truly shocking.”
But some Sheffield residents said they were happy to see people enjoying life again after lockdown.
Nicola Bradley posted: “Endcliffe Park has got a pretty big field there so I think as long as people are well spaced out and using their brains, sticking to the rules, I don’t see a problem with it.
“But let’s not forget that there is still Covid out there.”