WHEN the water level of the stream falls, the force
of the current is reduced and, in spite of the flow from one level to another, there are pools where a sort of stagnation takes place. Between one rainfall and the next a sufficient quantity of water never reaches these places, and in the eddies and deeper corners away from the inflow and the out- flow, the contamination that breeds flies and mosquitoes progresses. I walked up our little stream one morning not so long ago, listening to the slow, half-hearted trickle of water among the stones, looking at the pools where there is no fish life, although years ago I believe it was fairly plentiful. It was a warm morning. The conditions were right for flies and little clouds spun and danced above the pools, while on the water itself a few black smuts moved and two or three ' skaters' ran to and fro from the swampy tunnels of banksidc weeds and grasses. A cloudburst would have changed all this in an hour and would have swept the countless larva and nymphs to destruction, but in the warmth of the rising sun the water produced its insect life, for even a bug, a water boatman or a caddis grub, has' its hour.
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