On many watersheds as the late Summer and early Fall approaches, water levels are low.  In low water conditions on small to medium sized rivers, trout will migrate heavily for food sources within the run they are accustomed to living in. 

With high water temps the trout may be found in the heavily oxygenated water specifically during the heat of the day.  Here they will find shelter, oxygen and food in nymphal form and opportunistically eat drowned terrestrials and the like. 

There are also many times when trout can be found keying in on surface food sources in the shallow tailouts during low water conditions.  Although this is a vulnerable place for the trout to be in low and clear water conditions, the trout are able to see better in the tailouts as their scope of vision is considerably better wide than upwards through the water column.  

Finding trout in the shallow tailouts keying in on the surface could happen any time of the day, however,  mornings to late mornngs and afternoons to evenings would suggest a bit more protection in the form of shadows.  

During the late Summer and early Fall the trouts diet is usually more opportunistic rather then selective as the aquatic insect hatches are generally minimal to light and the trout will search out other food sources on the surface.... specifially terrestrials.  

One last note for the tip of the month;  Windy days are ideal for the terrestrial food seasons as this weather factor can dramatically increase the amount of surface food for the trout!