WARNING - you must be totally self sufficient. There are no shops or rubbish bins so you must take what you need to eat and drink and bring your rubbish out with you. Take plenty of water - there are no taps. Sunscreen and insect repellant too!
The walk is not difficult but you need to be on the go and not dawdle too much admiring the views. From Bark Bay to The Anchorage is 3 1/2 hours plus a short ime to rest and eat your lunch. The boat will NOT wait for you as it has a schedule to keep. However they do a head count and know that you are there and if you should miss the boat for any reason someone will come to get you.
After all of that - DO IT! it is great and the scenery is stunning!
New Zealand has the highest rate of skin cancer in the world. Though there are places in the world that get more hours of sun it is more intense in NZ for three reasons. The UV levels are higher because of the closeness of the sun in the summer,a thinner ozone layer over NZ and most surprising to me, New Zealands amazing clean air makes people more vulnerable to sunburns because pollution can actually block ultraviolet rays. Doctors advise to avoid sun exposure and always use protection. Though this is common in Southern California where the suns shines over 3,000 hrs, the rate of Kiwis having skin cancer is double even though their sunniest locations (Nelson region being # 1) gets closer to 2,000 hrs of sun a year. In California the sun is strongest between 11:00 and 2:00 PM in NZ they have longer daylight hrs and the sun is considered strongest between 11:00 and 4:00 PM.