Sometimes people are so fascinated in something, for example the stalactites, and feel the need to take a souvenir in memory of the great experience. This is not sustainable as the time period for the decorations to grow back is beyond repairable, as on average, the stalactites only grow one cubic centimeter every century. When tourists travel throughout the caves each person emits 170W of energy into the caves, which can interfere with the humidity levels in the natural environment and also disrupt the eco-system inside the caves also.
When anyone touches the structures of limestone within the caves, finger prints contain acidic oils, which over time, would break down and ruin formations within the caves. For example, in the 1970's, an average of 4 tours each day, with up to 100 people at once, caused reduction in glow worm numbers and eroded the limestone formations due to people touching the structures within the caves. When people breathe, we breathe out Carbon Dioxide which is also slightly acidic, and with 400,000 people going through the caves each year, it can pose a huge risk on the humidity levels increasing or decreasing dramatically and disrupt the eco-system within the caves.
The caves natural environment is dark with no lights, however, for anyone travelling throughout the caves to see, they must have light. The lights from torches etc, have negative impacts on the limestone formations, that over time build up with a moss-like substance called Lampe flora. The interaction between rainfall in the above ground environment and the stream running through the caves causes approximately 4-10 times a year, for the Black Water Rafting and glow worming activities to be closed due to flooding, which effects both the environment by eroding the caves structures, with faster moving currents and also a loss in the economic factors of the Waitomo industry, and on the people, with disappointment felt among the tourists and employees/tour operators.
I think that the caves are a beauty waiting to be explored but they should be explored in a sustainable manner and efforts shall be taken to keep the place alive.