The lake is in a reasonably remote part of the country, in an area with exceptional high rainfall. Plenty of other sources of water. Most of that fresh water wa

The lake is in a reasonably remote part of the country, in an area with exceptional high rainfall. Plenty of other sources of water. Most of that fresh water was going to flow out into the ocean anyway, this just sends it via a more direct route. The longer route (which actually flows next to the farm my mum grew up on) doesn't even go near a major population centre. The largest town (Tuatapere) has a population of 500 people.