An autumn working bee organised by the Ruby Island management committee on Sunday found the island's only toilet was full despite being installed in June last year with an estimated four years of use before having to be emptied.
Ruby Island management committee co-ordinator Jude Battson said the $10,000 toilet replaced a long drop that had served the island for 17 years.
This was the first year the toilet had been used to that extent and it raised a question as to why, she said.
New part-owner and operator of Lake Wanaka cruises Tim Cuthbertson said he had offered a daily cruise and private charter to Ruby Island since taking over the company before Christmas.
As the island was a public reserve managed by the Queenstown Lakes District Council he was not required to obtain a concession to go there, he said.
On Sunday, he took a private charter of about 20 Japanese tourists to the island on his 16m catamaran, as well as passengers on the regular daily cruise in the morning.
''Some tourists only want to go on a short trip on the lake. The Ruby Island cruise is good for that and also young mothers with younger kids who want to enjoy somewhere close where you can go on a short walk.''
Mr Cuthbertson said that he would like to see guard rails placed around the ''steep drop-offs'' as he believed it posed a public safety risk.
Ms Battson said any proposed changes to the island would require a ''conversation with council'' and a ''plan that would need to be approved''.
A QLDC spokeswoman said the council would be checking whether the charter operator's increased visits to Ruby Island reached the threshold to require a resource consent or permit.
-By Kerrie Waterworth
