by Fly Fisherman

Weather and barometric conditions as well as the time of day influence both the places in a stream where you will find trout and what the fish will be doing. In most cases none of these things influence the fish in a trout stream as much as the water temperatures, the stage of the water, or the hatches of available aquatic insects; but they still are important.
In most cases, fish go into deeper water when the barometer is falling, and into shallower water when the barometer is rising. This effect is much more pronounced in lakes and ponds than in streams, because of greater differences in depth, but it applies to rivers as well. Stormy weather usually occurs when the barometer is falling. A rising barometer normally indicates good or going-to-be-good weather. Fish will, as you would expect, usually go to deeper water in stormy weather and come to shallower places when the weather becomes normal.
Other things being equal, trout will be more likely to feed freely when the barometer is rising and the weather is normal than in stormy weather with a falling barometer. However, very often a change in the stage of water (higher or lower), or a change in water temperature will reverse this trend.
The commonest case on a trout stream is when the barometer is falling and stormy weather is coming on accompanied by a rise in the water level that washes a lot of nymphs and larvae off the rocks of the rapids and into the current. This influx of food causes the trout to go on feed—but near the bottom and mostly in the deeper water.

There also appear to be certain periods at different times of the day and on different days—called solunar periods—during which fish feed more freely than at other times. The same natural factors which control tides apparently control these solunar periods. My friend, John Alden Knight, a great fisherman and writer, has made a life study of solunar periods. I always take a copy of his Solunar Tables along with me on fishing trips, and try not to miss being on the lake or stream during the best solunar periods. You don’t always find good fishing then, because water temperature, weather, stage of water and fish food conditions may reverse the solunar period influence, but I’ve found it always pays to take these feeding periods into account.

When the water temperature is between 600 and 68°, the time of day makes quite a difference in the feeding habits of trout. Contrary to what happens when the water is colder, the fish are more liable to stay in shady spots during the middle of the day and go into the shallow feeding positions in the evenings, early mornings and at night. This tendency gets more pronounced above 65° water temperature. Above 66° you will find trout during the day in the fast, more highly aerated waters—just under small falls and in shady spots below riffles.

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