1922.] Fauna of the Chilka Lake : Observations in Rambha Bay. 683 



water having a density of g - o or over was found only at the mouth of the bay and 

 in a small area in the southern prolongation of the head of the bay to the south-east 

 of Rambha village ; throughout the whole length of the ba}^ the density was found 

 to decrease steadily as we approach Rambha village, and the contour lines of equal 

 density drawn on the plate show very clearly that this fall is due to an influx of 

 fresh water. The map shows that at the head of the bay in the vicinity of the village 

 two streams enter the lake and at this period of the year, and even on into Decem- 

 ber a quantity of warm fresh water was being brought down, which flowed out into 

 the lake over the top of the more dense water below. As this current of water passes 

 out into the lake its own density is raised by gradual admixture with the denser water of 

 the lake, while at the same time the salinity and consequent density of the lake- water 

 is diminished, and the effects can be traced even as far as the mouth of the bay. 

 The effect of this surface current of fresh and comparatively warm water is seen 

 extremely well in sections 1 and 2, plate XXXII, at stations 14 and 20 respectively. 

 The current runs from near Rambha village across the mouth of the southern conti- 

 nuation of the bay towards Ganta Sila, and in August its course was plainly marked 

 b}^ floating leaves and scum. At this point the current alters its course and sweeping 

 round the northern promontory of Ganta Sila appears to divide. A study of section 

 4, plate XXXII, shows that we have two areas of lower density situated at the two 

 sides of the entrance to the bay, at stations 8 and 11 respectively, and, furthermore, 

 in both these areas the temperatures recorded are higher than that of the surrounding 

 water. That the lowered density is not merely the result of this raised temperature 

 is, however, clearly shown in section 4, plate XXXIII, in which I have plotted out 

 the densities after reduction to standard temperature. One area of lowered density 

 occur on the surface at station 11, and it has a temperature of o - 2°C higher than the 

 surrounding water, while at a depth of 6 feet the temperature is as much as 0'6i° 

 higher than the water at the corresponding level at station 10. This area is a direct 

 continuation of the surface current noted above and on a calm day the course of the 

 current could be easily traced from Ganta Sila to the south-west corner of Barkuda 

 Island by the presence of the leaves and scum referred to above ; it is obvious 

 that any breeze from the S.W. or S.S. W. will very materially assist, even if it is 

 not the actual determining factor, in the causation of this current. A strong breeze 

 will cause a flow of surface water of low density out of the bay and this must natu- 

 rally be compensated for by an influx of water from outside the bay at the deeper 

 levels. At station 8, the second area of lowered density is found, not on the surface, 

 but at a depth of from 5 to 6 feet, and in order to account for its presence at this 

 depth we must first study the conditions existing in the deeper waters of the lake. 



One of the earliest points that attracted my attention during my survey was 

 the extremely rapid rise in the density of the water of the bay as we pass from the 

 surface towards the bottom. This alteration of density is most marked, as one 

 would expect, at stations 13, 14 and 15 at the head of the bay where owing to the 

 influx of fresh- water the surface density is markedly lowered, and in this region a re- 

 ference to section I, plate XXXII, shows that the density in situ increases from 4-46 



