Lake Musters and Lake Colhué Huapí (45°25′S 69°11′W, at altitudes of around 260 metres (850 ft)) form the terminal stage of the Senguerr River endorheic basin, located in the patagonic central region of Argentina in the south of Chubut province. Closest populated area is Sarmiento, an 8,000 inhabitant former Welsh immigrant colony. The lakes gave their names to the Mustersan and Colhuehuapian South American land mammal ages.

This lake, once called Otrón by the ancient tehuelches^{[citation needed]}, received its current name in 1876 from naturalist and geographer Francisco Pascasio Moreno who aimed to honour the Patagonian adventurer George Chaworth Musters.

Musters occupies a Cretaceous conformed depression in the central Patagonic mesa in the Golfo San Jorge Basin. It receives the highly branched inflow of Senguerr river by its southern coast after a 350 kilometres (220 mi) voyage from the Andes. Several of those branches reach lake Colhué Huapí by a sinuous course called Falso Senguerr; the only permanent one feeding such lake.

The lake is of tectonic origin, with average depths of 20 metres (66 ft), which gives a deep blue water hue. It is considered mesotrophic, based on its nutrient and algae mass (<5.2 g/m³ or 0.0088 lb/cu yd). Musters presents an abundant aquatic fauna comprising Patagonian perch (Percichthys trucha) and patagonian silversides (Odontesthes microlepidotus). Also, as is the case with most Patagonian lakes, foreign salmonidae have been implanted, like Salvelinus fontinalis, rainbow trout, and in lesser amounts, Salmo fario. These species have added environmental pressure over two native species nowadays endangered in the lake (Diplomystres viedmensis mesembrinus and Galaxias platei).^[1]

• Lake Musters
• Paragliding at Lake Musters.

Quick Facts Location, Coordinates ...

Lake Colhué Huapí
Lake Colhué Huapí
Location	Chubut Province
Coordinates	45°29′38″S 68°45′26″W
Type	endorheic
Primary inflows	Senguerr river
Primary outflows	evaporation
Catchment area	10,900 km2 (4,200 sq mi)
Basin countries	Argentina
Max. length	50 km (31 mi)[2]
Surface area	810 km2 (310 sq mi)
Average depth	2 m (6 ft 7 in)
Max. depth	5.5 m (18 ft)
Water volume	1,620 hm3 (1,310,000 acre⋅ft)
References	[2]

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The name of this large water mirror comes from the Mapuche language Mapudungun. Colhué means "reddish or red place" and Huapí means "island".^[3] It is a reference to one of the many clay conformed islands of such lake.^{[citation needed]} The lake was named in official Argentine cartography by explorer Francisco Moreno who reached the lake in 1876.^[3] Subsequent analysis have shown that Moreno appear to have mistaken it for the larger General Carrera Lake whom indigenous Tehuelches called Coluguape.^[3]

Colhué Huapi fills a shallow depression formed by strong eolean action over an area of fine clays. It is fed by the Falso Senguerr river, a sinuous branch of main Senguerr River. The lake coast is dominated by extensive wetlands mainly at its feeding zone. In contrast to its neighbour Musters (separated by a 12 kilometres (7.5 mi) wide and 695 metres (2,280 ft) high isthmus) Colhué has an average depth of 2 metres (6.6 ft) and high water turbidity due to suspended sediments deposited by constant wind.

It is considered an argilotrophic brackish water lake because of its high levels of inorganic sediments in suspension. As with lake Musters, and despite the high water opacity, Patagonian perch and silversides have large populations. Of high interest is the native big mouth perch (Percichthys colhuehuapensis) currently^[when?] endangered by pressure of human-introduced foreign salmonidae.

• Lake Colhué Huapí
• Fauna present at the Lake Colhué Huapí.

Several water offtakes have been progressively placed at lake Musters for drinking water supply, as well as many diversions of the Senguerr river to feed oil extraction facilities in the nearby region. This complicated the already resented water balance of the whole system to the extent of near-collapse at Colhué Huapí, whose peripheral surface continuously retracts and dries.^[4] The hydrological equilibrium of the whole basin has been negative in the past seventy years.^[when?] Currently^[when?] these lakes' situation could be defined as compromised.