I am not associated with this shop in any way, but here is a description of the issue by a local guide/shop owner:
Fishing Conditions on the Arkansas River Lower Basin in Colorado
I found it an interesting read, below is the "meat" of what he is saying IMO.
Start Quote from Greg Felt, ArkAnglers:
In April of 2008, just as the caddis hatch was progressing into Cotopaxi and Coaldale, flows on the river rose precipitously. This was in part due to spring storms, but was followed by releases from Twin Lakes, leading to a prolonged flow of high and cold water. As caddis larvae from segments of the river in Bighorn Sheep Canyon had already gone into pupation, sealing themselves in their cases and passing through their metamorphosis, they were not able to continue feeding themselves and by the time warmer water eventually returned, many of them had expired without hatching. Further upstream, many caddis never even pupated at all. The result was a crash in the brachycentrus population between Cotopaxi and Buena Vista. There were bugs that survived and reproduced, but they were in greatly reduced numbers. The population has survived, but not flourished, since then.
A common thought among anglers familiar with this situation is that other bugs have replaced the caddis in their ecological niche. This may be a logical conclusion to reach, given the burgeoning diversity of our aquatic insects, and particularly among the stonefly and mayfly orders. However, I believe this is most likely a correlation without causation. Cased caddis are extremely hardy creatures – that is why they thrived in the metal-laden waters of the pre-Superfund Arkansas River. The fact that the improved water quality supports a broader insect population should not mean that the caddis are now at a disadvantage. I think it simply takes a while for a population like we’ve historically had to rebuild itself.
There are another 2-3 paragraphs about the situation on the website referenced. I am planning to float somewhere in the area between BV and Rincon (not sure of exact segments yet) on Saturday 5/4 and Sunday 5/5, so I will add any personal observations after this weekend. I am not sure of the situation on the Eagle, but it easily could have been caused by a similar warm period early in the spring followed by high/cold water as described above.