Located in Nelson Lakes National Park, Blue Lake—also known as Rotomairewhenua—holds the title of the world’s clearest lake. Scientific tests carried out in 2011 by New Zealand’s National Institute of Water and Atmospheric Research (NIWA) showed Blue Lake to be the clearest natural body of fresh water known to man. According to the NIWA research results, visibility in the lake is up to 80 metres (262 ft) – meaning the water is considered almost as “optically clear” as distilled water.
Blue lake is characterised by blue-violet hues seen only in such clear natural waters. Part of the Nelson Lakes National Park conservation area in the northern South Island, Blue Lake is fed by waters from nearby Lake Constance.
The park is a popular hiking, fishing and destination. The lake is a two-day hike from the park boundary or, for an aerial view, there are scenic flights with Reid Helicopters.
The spring-fed source of the water, and its 1200 meter (3937 ft) altitude above sea level, just below the tree line of stunted mountain beech, ensures that Blue Lake is always cold, ranging between 5 and 8°C. These astonishingly clear waters are regarded by the local Māori iwi / tribe as tapu or sacred which means that humans are not permitted to enter the lake.
However, in early 2013, Danish photo-journalist and environmentalist Klaus Thymann was granted special permission by Māori, NIWA and New Zealand’s Department of Conservation to capture the clarity of the lake for conservation purposes.
Nelson Lakes National Park begins at the northern end of the Southern Alps and the port city of Nelson is the nearest main centre. The national park, formed in 1956, covers some 1020 sq km (393 sq miles), and is popular for camping, tramping and fishing. There are remote mountain passes to challenge the experienced solitude-seeker, but the lower reaches offer accessible hiking trails and overnight, camping and fishing.
The park is home to the Rotoiti Nature Recovery Project, which aims to revive populations of kiwi, other native birds and lizards.
Blue Lake / Rotomairewhenua is on the multi-day Travers-Sabine Circuit track. The 80 km (50 miles) hiking route through Nelson Lakes National Park reaches deep into the national park, through forests surrounded by 2000 meter peaks.