He said he didn't know who had taken the large sign, but it could have been one of the people who had used the land before it returned to the trust.
"It might have been any of those people who think they have more rights to this land than we do."
A steel sign was also taken in 2013, while the land was still leased to Fish and Game.
He said the trust had not decided how long access would be blocked. They would be discussing it at a meeting at the lake this weekend where they would be assessing their future plans.
In December the trust had said they would be blocking public access for safety reasons while they worked to restore the area.
Their vision to restore the area included removing willow trees, removing grass carp, eliminating hydrilla weed from the lake bed, and restoring the wetlands with native flora and fauna.
The trust also planned to place a rahui over the northern end of the lake.
Guthrie Smith Trust Arboretum curator George Christison said not many people used that end of the lake, so he didn't think the blocking of access would affect many people.
"It's their land and so it's their prerogative, the public have access to a lot of the lake they can use," Mr Christison said. Nearby resident Cathie Turnbull said she owned shares in the B5 section, and used the track to access her farm during the winter.
"We need to use that because if we don't have access we can't get to our animals, and we can't feed them."
She said when willow trees had blocked the track in the past she had just moved them with her tractor.
