The theft had saddened her.
"The whole point of the station is to protect our taonga that's going to become extinct if we don't look after it," she said.
Kauri forests once covered 250,000ha of Aotearoa. Now just 1 per cent remained, and that was under threat from kauri dieback.
"They just haven't thought about the consequences of their actions. If people come here from another forest and they can't clean their shoes it could mean the death of these trees. I don't know how they can be so thoughtless," Ms Schmid said.
DoC Bay of Islands senior ranger Marty Akroyd agreed that the theft put kauri at risk.
"We'll have to fix it as soon as possible. We may have to put in bottles and brushes until it's replaced," said, adding that DoC would consider how to make thefts more difficult in future.
Drench guns had previously been stolen from the Forest Pools hygiene station, near Ōkaihau, but this was the first time a tank had been taken.
The theft was reported to the police in Kerikeri on Friday. Anyone with any information is asked to report it to the police on 105, or via Crimestoppers, anonymously, on 0800 555-111.