It is fenced off but there will be parts of that mud pool that are cooler and your able to bathe in as the heat is not consistent throughout mud pools but rather more concentrated to certain points. I've been to this particular mud pool which is in wai o tapu. There is an elevated lookout up top and if you go through the bush and follow the track you will come out on a forestry track. Hang a right and follow the track for about 100 meters and on your right you will see two geothermal heated lakes a big one and a small one. I've swum in both those lakes one is more pleasantly warmer than the other and what's really cool is there is a big silky soft mud bank in between the lakes and the mud is so soft and you can just chill there and enjoy the warm mud and venture into either lake to rinse off. I think I'm the only one to swim there though cause I'm adventurous like that. I also took my friend who was visiting from Chile and my nephew lol.
