31 



in Saldanha Bay about the year 1907 and near Stumpnose Bay 

 about 1869. To this category may also be added the case of 

 the " phosphorus " in Table Bay about 1888. In the occur- 

 rence at Swakopmund in 1880 the peculiar red (" bliitig") colour 

 of the sea would seem to indicate that there was at least some 

 element of this nature present here, though it is to be noted 

 that the colour of the water was described by another observer- 

 some months after the occurrence as " inky." This, together 

 with the fact that at the somewhat similar occurrence in the 

 neighbourhood (Wallish Bay) there is no mention of red water, 

 seems to indicate that, if present, it was not the main factor 

 in the disturbance at Swakopmund. 



There seems, however, to be no doubt that in some instance 

 decaying masses of Noctiluca (" red water ") is the immediate 

 cause of the death of fish by suffocation, though there re- 

 mains to be accounted for the cause of the accumulation and 

 dying-off of these animals. 



The second apparent cause of such phenomena is the pre- 

 sence of vegetable matter (diatoms) in masses, leading to 

 decomposition and consequent suffocation of sea animals. 

 This appears to have happened in the occurrence at Schell Bay. 



The main factor in the occurrences at Walfish Bay also seems 

 to have been the decay of diatomaceous matter in the bottom 

 of the bay in enormous quantities, a sample of the mud at 

 the bottom of the bay having been found on microscopic 

 examination to consist almost exclusively of diatoms. 



The occurrence at Knysna will not, however, admit of any 

 such explanations. There is no record of the presence of 

 Noctiluca in large quantities either in the sea or the lagoon. 

 Here their absence in quantity may be accounted for by the 

 fact that there is here no chance of the water remaining in an 

 undisturbed state, as the currents in the sea are strong and the 

 entrance to the lagoon is very narrow. Special enquiries 

 were made as to whether " red water " was ever found in the 

 lagoon, and it appears to be unknown. 



The explanation generally accepted at Knysna is that the 

 death of fish is due to cold water, as it is always associated 

 with the presence of such water. The occurrence is annual, 

 and in a more or less marked degree, so that it may be accepted 

 as a statement of fact that the fish die off when the cold water 

 appears — whether from the actual cold or not is a different 

 question. Further, it is observed on such occasions that the 

 cold water is of a distinctly different colour from that of th 

 normal sea water, so marked that ordinary fishermen recognis 

 it readily and expect to find dying or dead fish in it. The 

 fishermen describe the cold water as of a muddy colour. *and 



* It is not associated with heavy rainfalls which often produce large areas of 

 muddy water in the sea. 



[C.P. 6-'i4.] 



