September, 1923. The Irish Naturalist. 80 



ALGAL DISCOLOURATION OF LOUGH NEAGH 

 AND THE RIVER BANN. 



BY DENIS R. PACK-BERESFORD, M.R.I. A. 



Great interest has been taken during this spring and 

 summer by residents in the neighbourliood of Lough Neagh 

 and the River Bann, and there has been some correspondence 

 in the Belfast papers, on the discolouration of the lough 

 and river. The curious and quite unusual colour of the 

 water was first noticed about January or February last, so 

 far as I have been able to ascertain, and began after the 

 river was in flood. Instead of clearing in the normal way 

 it gradually assumed a greenish hue, and eventually a 

 greenish grey colour which lasted for months, and it was 

 still of the same peculiar colour when I first saw it towards 

 the end of May. One old man I met on the banks of the 

 river told me he believed that a " volcano " had burst in 

 Lough Neagh as the river had never been seen this colour 

 before in the memory of the oldest inhabitant. 



I at once got a glass of water out of the river to study, and 

 found it was perfectly clear with no signs of mud in it at all, 

 but on examining it with a pocket lens I found it to be full 

 of very minute floating hairs which were evidently an alga 

 of some sort. I put the glass of water to stand in the sun, 

 and in the course of a few da^^s several cotton wool-like 

 tufts began to appear in it, this evidently being the plant 

 growing. 



About the middle of June I took some of this water over 

 to London and to the Natural History Museum, where 

 Miss Lorrain Smith and Mr. Gepp very kindly examined it 

 for me and pronounced it to be an alga known as Oscilla- 

 toria tenuis, Agardh. 



They referred me to Cooke's British Fresh- water Algae 

 where" this plant is described as Oscillator ia aeriigescens 

 Hass, but told me that this is now recognised to be a 

 synonym for 0. tenuis. 



