My good friend and I were flaoting the upper Yellowstone River yesterday when we encountered a number of sizeable fish rising agressively all around us. These were not small trout by any means, and some of these fish were coming completely out of the water while others looked as it they were savagely attacking something on the surface of the water, or just below it.

For the most part, these fish were in relatively large, deep, slow moving water, but there were other similar rises just across the river from us where the water was shallower.

This happened in the early afternoon. The temperature was pretty warm, in the mid-80's, there was some cloud cover but no rain, and just a slight breeze.
We couldn't see any noticeable insect hatches, and nothing of any significance on the water's surface to trigger these rises.

I've encountered this twice before on the Yellowstone River, once 2 weeks ago, and another time a couple years ago. Both of the other times were much different weather conditions - cool, cloudy and rainy.

My friend was able to get one smallish Cutthroat trout fooled on a black foam ant during this feeding frenzy, but I don't think that it was terrestrials that caused the fish to rise in that manner (grasshoppers didn't work at all for them yesterday during this frenzy, although my friend caught a very nice brown trout on a big streamer when we saw those rising trout 2 weeks ago - and that was probably just coincidental to the agressive fish rises.)

Anyone have any knowledge or thoeries of what caused those fish to rise like that?

John

p.s. We did catch some other nice fish yesterday, including one big brown trout that smashed a hopper pattern, and jumped several times before being netted and released.)