On the canal oil thing clearly some commercial operation is putting waste oil into a drain which they should not be doing at all (even if its a foul sewer) . The sewer may be blocked by the fat and if its a very old sewer there may be an overflow into the canal. Or maybe they are using a surface water sewer which is even worse.
Any oily contamination like this will easily be spread by the wind and by any flow, however small that flow may be, in the canal.
Hopefully the source of the oil will soon be discovered by the relevant authorities.