icj22.J Fauna of the Chilka Lake : Observations in Rambha Bay. 689 



of silt-laden water brought down into the northern end by the branches of the Maha- 

 naddi System had expelled all that of higher salinity — a phenomenon already noted 

 with reference to the outer channel. It is evident that, in these parts of the lake, 

 the changes are not due to admixture so much as to the expulsion of one volume by 

 another." They appear to have overlooked the possibility that the fresh-water com- 

 ing into the lake might flow over the top of the denser water, and thus produce the 

 diminution in the density that they found during the monsoon months, and since all 

 their observations were confined entirely to samples taken from the surface, it is 

 impossible to say whether the same rapid rise in density as we pass from the surface 

 to the bottom, such as we have seen to be present in Rambha Bay in August, 191 9, 

 and to a less extent though still recognisable in April, 1920, existed at all in 1914 

 though I see no reason to suppose that it was not present at any rate to some degree, 

 or that it is a phenomenon confined to the area at the south-west end of the lake. 



On the occasion of both my visits we obtained evidence that this bottom layer 

 of denser water is steadily flowing into Rambha Bay from the main area of the lake. 

 This inflow was vastly greater in August, when the lake was rising, than it was in 

 April, and it seems probable that there are two factors concerned in its production. 

 The first of these factors is in my opinion the steady and continuous breeze that 

 blows throughout the greater part of the year across the lake from the south-west 

 or south-south-west. We have already seen that the effect of this breeze is to 

 produce a strong surface current out of the bay, and it is to this that I attribute the 

 deep influx of water of higher density into the bay along the bottom that was occurr- 

 ing in April, 1920. In August, 1919, however, the effect was too great to be accounted 

 for by this agency, and was, moreover, accompanied by a rise in the surface level, and 

 it seems to me that we have here evidence of the ' banking up ' of the more saline 

 water, as far as the deeper layers are concerned, such as Annandale and Kemp (loc. 

 cit., p. 11) postulated in 1914. 



The steady influx of fresh water from the Mahanaddi and local streams causes 

 a correspondingly steady fall in the density of the lake water so that the minimum 

 appears in a normal year to be reached about February when the influx of salt water 

 from the sea takes place, and a corresponding rise in density follows, reaching its 

 maximum about July, during which month Annandale and Kemp found the densit}^ 

 in Rambha Bay to be as high as 145 to 15 'O. During the period of my observations 

 in 1919-1920, we have two outstanding features of great interest. As I have already 

 mentioned between the months of August-December, 1919, the density of the water 

 in the bay had fallen very considerably, till at the end of the year the density at 

 standard temperature of a sample taken off Breakfast Island was only 2-19. In 

 April, 1920, the density of the water off Barkuda Island at standard temperature 

 had risen to more than twice this and varies from 5*5 to 6t. There had, therefore, 

 been no appreciable influx of fresh water into the bay and presumably into the whole 

 lake, and the explanation of the raised density combined with a marked lowering of 

 the surface level that existed in April seems to be found in the absence of the normal 

 inflow from the sea, which usually occurs in February and March, combined with 



