The park, in Middle Swan, has provided temporary homes for the residents whose homes were razed but the source of the illegal flare remains a mystery.
The fire tore though the banks of Blackadder Creek, which staff had been revegetating with native plants over the past year.
Owner Michael Repacholi said residents had mandatory insurance policies and the fire could have been far worse.
“If the wind was going the other way it could have wiped the whole park out,” he said.
He said staff members were quite upset about the creek after all the effort put in to restore parts of it, but they would persevere with their environmental efforts.
Midland Tourist Park is one example of about 60 fires around City of Swan deemed deliberately lit or suspicious since December.
The spate of arson attacks has Department of Fire and Emergency Services and the WA Police reaching out to the community for help monitoring the area.
Emergency services are asking residents to report any suspicious behaviour that could be linked to arson by calling Crime Stoppers on 1800 333 000.
Rewards of up to $50,000 are offered for information leading to the identification and conviction of arsonists.