Introduction

Fiordland underwater is globally unique. This uniqueness arises from a combination of factors including high mountains, heavy rainfall and the presence of temperate rainforest. In places Fiordland receives over 750 cm (300 inches) of rain a year. This water runs off through the leaf litter and picks up humic substances and tannins which stain the water a beer or tea colour. The runoff reaches the sheer sides of the fiords in spectacular manner. The response to rain is almost immediate with the creation of hundreds of waterfalls.

Doubtful Sound at sunrise can be an inspiring sight. (13.38K)

This waterfall, not far from Milford, is on the site of a giant treeslide that blocked the road for several weeks. Normally the hill side is dry. When it rains heavily it turns into a raging waterfall. (30.42K)

The Four Sisters in Millford Sound roar into life after rain. Their response is almost immediate and ends almost as quickly. Catchments are so steep and so small that that the waterfalls stop within a few hours of the rain stopping. (39.00K)

The (Lady) Bowen Falls tumble 160m (526 feet) from a hanging valley in the Darran Mountains. (72.97K)

"Classic" Mitre Peak reflected in tidal pool. (55.92K)

Because this darkly stained freshwater is lighter than the seawater in the fiord it forms a floating layer on top. Some mixing does occur so the layer is referred to as the Low Salinity Layer (LSL). As there is a constant inflow down the length of the fiord, the LSL moves steadily towards the sea being replaced at deeper levels by sluggishly flowing fresh seawater. In effect the fiord becomes a horizontal estuary. In times of drought the LSL may be almost non-existent and during heavy rainfall events it can be as much as 15m. The LSL averages 5m thickness and its effects on life in the fiord are dramatic. Click here for diagram of the low salinity layer

The most immediate impact is a huge reduction in light levels. Typically light levels just below the LSL are around 10% of light levels at similar depths in the open sea. This "fools" (for want of a better term) deep water organisms into living at shallow depths. Black corals can be seen at depths as shallow as 5m.

The underwater environment in Fiordland is characterised by ghostly white coral and clear, green, water. (53.37K)

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Last modified on Monday, September 04, 2000