Photos sent to The Observer by a Summersdale resident show rubbish strewn across Oaklands Park.
The resident, who wished to remain anonymous, said he was alerted to rubbish while out walking his dog on Saturday (July 13).
He said: "I've seen them there before. It's a site they have been to before and they left behind a disgusting mess.
"Furniture, children's toys, clothes, litter, food wrappers and around the corner is a place they were using as a toilet."
The man described the 'toilet' area as 'smelly and offensive' and said there was 'evidence of human faeces'.
He added: "And on the site that is next door to Chichester's famous theatre — it's not a great advert for the city. I thought 'not again'. No-one would mind if they cleared up after themselves.
"Normally when they park on council property they move them on quite quickly. It's private owners that have a lot more difficulty."
It comes after travellers reportedly moved onto Tangmere Airfield. Read more here: Travellers with 16 vehicles 'move onto Tangmere Airfield'The Summersdale resident believed the travellers had been based in Lavant before moving to Hunter's Race then onto Oaklands Park.
A spokesman for Chichester District Council, which is responsible for the site, said: "There were travellers on Oaklands Park, but they have now moved on. We have cleared the site of all rubbish."