The predations of today’s influx of visitors and the operation of a small fishing fleet have necessitated strategies to preserve the fragile ecosystem. Like all fiords, Milford Sound has an entrance sill at its mouth, in this case only 70m below the surface – by comparison, the deepest point is almost 450m. This minimizes the water’s natural recirculation and hinders the mixing of sea water and the vast quantities of fresh water that pour into the fiord, creating the strange phenomenon of deep water emergence. The less-dense tannin-stained fresh surface layer (generally 2–6m deep) builds up, further diminishing the penetration of light, which is already reduced by the all-day shadow cast by the fiord walls. The result is a relatively barren inter-tidal zone that protects a narrow – but wonderfully rich and extremely fragile – band of light-shy red and black corals; these normally grow only at much greater depths, but thrive here in the dark conditions. Unfortunately, Milford’s fishing fleet use crayfish pots, which tend to shear off anything that grows on the fiord’s walls. A marine reserve has been set up along the northeastern shore, where all such activity is prohibited, but really this is far too small and conservation groups are campaigning for its extension.