Lake Matheson

Lake Matheson is a small glacial lake in South Westland, New Zealand, near the township of Fox Glacier. It was a traditional food-gathering place for local Māori. An easy walking track circles the lake, which is famous for its reflected views of Aoraki / Mount Cook and Mount Tasman. Geography Lake Matheson formed between two moraine terraces left by the rapid retreat of Fox Glacier / Te Moeka o Tuawe 14,000 years ago, at the end of the last glacial period. The retreating glacier left behind a valley and a huge slab of ice insulated by a deep layer of moraine gravel, which gradually melted and collapsed to form the lake bed. The lake is now about from the current terminus of the glacier in the Southern Alps. Moraines, outwash gravels, and river gravels dammed the valley, and the lake grew, fed by small streams and seepage – there is no major river inflow or outflow. Lake Matheson is 30 ha in area, with an approximately 1.5 km shoreline and an average depth of 12 m. The streams that feed it pass through dense native bush, and often accumulate foam after heavy rains. They carry organic matter and tannins from the forest, which colour the water a dark brown – this is the factor that limits visibility and enhances the mirroring effect from the lake. The lake water is acidic (the pH has been recorded as low as 5.5), low in nutrients, and sometimes almost de-oxygenated. These are all characteristics of a dystrophic brown-water lake that is accumulating organic matter; in the long run, the lake will gradually fill in and become a peat bog.