Waikoropupu Springs

Pupu Springs are among the largest freshwater springs of the world! In 1989 they were ranked 24th in the world among Karst springs. They are also famous for the visual clarity of the water. In a scientific examination in 1996 the average black-body visibility was determined to be 63m. This is the highest yet reported for any fresh water, and close to the theoretical maximum for optically pure water. The extreme optical purity, which is uncommon for karst water, is interpreted as a result of the long residence time between aquifer recharge and re-emergence in the springs. According to Williams (1992) the water stays underground roughly three to eight years.

The water of the springs is full of fish, like the welcome swallows (Hirundo tahitica neoxena), brown trout and some salmon that escaped from nearby farms. The largest basin of the spring has more than 40m across, but there are a number of smaller springs. The floor of the basins is covered with white sand, which is thrown up by the the force of the spring water. This dancing sands make it easy to determine where the vents are located. The springs have an enormous energy, especialy the narrower vents. This is a result of the enormous amount of water, which is about 14,000 litres of water per second or 1,200,000m≥ per day. This would be enough to supply a big city.

The old question, where all this water does come from, was answered in the 20th century by dyeing experiments. The water comes from the Takaka river and his tributaries, which flow over karstified marble to the south of Pupu springs. The water enters swallow holes and flows through a huge cave system to this resurgence. Sometimes during summer the Takaka river is swallowed completely, some 15km up the valley near Lindsay's Bridge.

But Pupu springs is only one of several resurgences of this underground stream. The cave system continues under the sea and there are three offshore springs. The karstified marble is enclosed between two water restistant rock layers, and so the water is transported far into the Golden Bay. The sweet water of the submarine springs is lighter than salt water, so it flows forcefully to the surface. But the heavier salt water also enters the cave system and mixes with the sweet water in the cave. It even reaches Pupu Springs, which has an content of 0.5% sea water.

Pupu Springs is located in a beautiful bush area with very interesting walks. Several large signs explain fauna, flora, history and geology of the springs and the area.