Fire chiefs are still to determine the cause of the blaze, but have not ruled out deliberate ignition.
But Mr Wallis was quick to point the finger at arsonists.
He said: “This is the third arson since we’ve opened. First, there was the zoo, then Casablancas [a bar and restaurant] and now the River Caves.
“I’m lost for words. All the work that we’ve put in to provide a fairground in Southport and it’s being destroyed by vandals. The weather over the last few days has been the best since we opened and now this happens. We don’t get any trouble when we are open, but as soon as the place closes all the bad boys break in. I’m gutted.”
Southport resident Dave Thackeray, 34, said: “The River Caves was one of my most-loved rides as a child. I had my first kiss there when I was 14. If it is arson, then I haven’t seen destruction on this scale in Southport for many years.”
The River Caves operated as part of the Pleasureland funfair which was closed in 2006.
The site was sold to Sefton Council in 2007 for £7.25m, with Dreamstorm granted a licence to run a temporary attraction on the site.
The site is to undergo an £80m overhaul as part of the town’s seafront redevelopment by 2014.