OK that link isn't the greatest but Brent will be able to decipher something out of it...
Not a whole lot except you ain't got much oxygen up there and it's getting worse.
I don't know that river, and it looks like it is really are reservoir which means not much current, not much open water. Lots of sediments and therefor lots of O2 eating bacteria.
Here in IA we get fish kills when a farmer makes a "deposit" on his personal sewer (generally a small river to most people). The big load of organic matter kicks the bacteria into high gear. They chew up the manure and all the O2 doing it, and that kills the fish. It's not the sewage that is toxic, it's the O2 deficit that the sewage causes that is the killer. Luckily around here, the farmer only pays for the fish he kills, so he generally has a big 1-time start up fee, but after that, if he is regular about it, there aren't any fish left to kill, so the cost is effectively zero.
Big sudden runoffs over frozen ground will sweep a lot of manure and other organics into the river unintentially and this same thing can happen but it's usually less dramatic. My river just jumped 12 vertical feet last Saturday, and we might be seeing low O2 but all the fish died last summer anyway.
