Crew members of TSS Earnslaw say there were "disgusted" to be confronted with the worst case of vandalism against Queenstown's historic steam ship in the past 12 months.
Owner-operator Real Journeys was upgrading its security after squashed food, litter, tobacco, damaged equipment and human faeces was found on board early on Tuesday.
It was the second alleged episode of vandalism since the $1 million survey and beautification of "the Lady of the Lake" was successfully completed last month, in time for its centenary in October.
Skipper Peter Greer said the penalty against the culprits "needs to be big enough so that they don't just see this as 'just a toilet prank', but as it is a direct threat to someone else's health."
Earnslaw and Walter Peak operations manager Angus Small said yesterday staff members had fully decontaminated the ship.