310 F. H. Stewart : Aquatic animals from Tibet. [Voi.. II, 



The first considerable mass of water met with is the Rham- 

 Tso (see plate xxvi), a lake situated about twenty miles from the 

 pass at an elevation of 14,700 ft. It is about eight miles long by- 

 four broad, and appears to be shallow throughout. It occupies the 

 whole of the north-eastern end of a broad plain which is surrounded 

 on all sides by mountain chains. The southern portion of this 

 boundary is the Chumolhari group of mountains covered with per- 

 petual snow. From April to October this lake is entirely free from 

 ice. In October ice begins to form round the margins and gradually 

 spreads until it covers the whole surface. The winter months are, of 

 course, intensely cold. During the summer, however, no climate 

 could be more delightful. In the daytime the temperature rises to 

 about that of an English summer's day and even at night remains 

 moderate, so ringed in is the plain by bare hills which store up the 

 sun's heat. During these months the Rham-Tso is well peopled. All 

 round its grassy banks, bar-headed geese rear their families, while 

 ducks of many kinds are to be seen on its waters. Fish are ex- 

 ceedingly plentiful, and large numbers are caught in nets set on 

 stakes across the outlet at the northern corner of the lake, where a 

 small river runs out to fall into Kala-Tso four miles to the north. 

 These fish are preserved by the Tibetans by being split like findon 

 haddocks and dried in the sun. They are not salted or smoked. 

 When fresh they are exceedingly good eating, the flesh sweet and 

 free of the muddy taste and the multitude of bones which render 

 Tibetan river fish so unpleasant. The dried fish are, however, not 

 for European taste. 



Water weeds grow in abundance for many yards out from the 

 margins of the lake, and Amphipods, Copepods, shells and a species 

 of Hydra flourish among this vegetation. 



From Kala-Tso, a lake closely resembling Rham-Tso, but on a 

 somewhat smaller scale, the water escapes under ground in the 

 direction of Gyantse. It reappears about twelve miles off near the 

 village of Mang-tsa (14,500 feet) and, reinforced by several small 

 streams issuing from springs on the hillsides, forms the commence- 

 ment of the Nyang Chu, the river which flows through the Gyantse 

 valley and ultimately falls into the Tsang-po. 



These streams are only completely frozen during the coldest 

 months of the year — February and March. The spring water is 

 sufficiently warm to keep ice-free for some miles during the rest of 

 the year. Here among the moss which grows in the small rivulets, 

 shells and Amphipods, Oligochsetes and Turbellarians abound. 

 Small loaches {Nemachilus stoUczkce) are also common. 



Twenty miles nearer Gyantse, at Kang-ma, is a group of springs, 

 the water of which is tepid and heavily charged with carbon dioxide. 

 The only animals found in these springs are certain Ostracods 

 {Eucypris minuta^ v. Dad.). 



In the Gyantse valley itself the river flows with considerable 

 rapidity. The water is grey and loaded with mud. It does not 

 freeze over even in the depth of winter, but from December until 

 April the surface is dotted with ice carried down from above. 



