Often in slow pools of two streams I fish trout rise, though there doesn't seem to be a hatch. They rise too frequently for me to assume they're going after terrestials.

A few days ago I read an article in which the author mentioned invisible hatches - midges so small that an angler can't see them without binoculars.

Is something like that really possible, especially in my case when I'm about thirty feet from the rises?

Thanks,
Randy