208 BRITISH FRESH-WATER FISHES 
at the end of the eighteenth century; and second, the 
inordinate pollution of the tidal part of the river. 
The first of these causes still exists in full force, but there 
is no reason to doubt that, were salmon to be seen attempting 
to pass over Teddington Weir, the Conservancy would 
acknowledge their obligation to erect passes over all such 
obstacles. This, then, is a remediable difficulty. The second, 
to those who remember the condition of the river from 
Chelsea downwards five-and-twenty years ago, might well 
seem insuperable. The pollution by sewage and refuse of all 
kinds culminated about the beginning of Queen Victoria’s 
reign in the discharge of the waste from gasworks, and the 
channel continued to get worse for several years, until all men 
declared it to be intolerable. The stench from the river along 
the terrace of the Houses of Parliament was overpowering and 
nauseating. Below Westminster Bridge a dark, malodorous fluid 
ran at low tide between exposed flats of black sludge. All that is 
now changed, By the joint and energetic action of the Thames 
Conservancy and the London County Council the Thames 
estuary is as pure as any salmon river need be. Of course the 
water is turbid, as is always the case in alluvial estuaries, but 
there is neither organic nor mineral matter in suspension to 
cause any injury to fish life. I can testify to this from 
personal inspection of the river from Westminster Bridge to 
Barking Creek. The black mud flats have disappeared ; the 
river margin, where clear of buildings, consists of bright flint 
gravel, clean sand, or ordinary alluvial mud. Why, then, it 
may be asked, have salmon not returned of their own accord ? 
The answer is that there is still a formidable obstacle to their 
entrance from the sea, arising out of the very means which 
have been adopted to cleanse the river of sewage. London 
sewage, as is well known, is pumped up at various stations 
within the town to such a level as will cause it to flow down 
to Barking. At Barking it is dealt with by precipitation ; the 
solid deposit and flocculent matter being removed and carried 
