Key questions if you could answer that would help an investigation:
Were the trout the only species seen as being dead?
If not, what other species were seen dead or distressed?
Were the dead trout primarily or exclusively the large ones?
What species, if known for certain was/were the dead trout? RT and BT or just one species?
Were any trout still alive and apparently healthy or alive but distressed?
Any obvious unusual coloration or substance in the water column or coating the stream bottom?
For others who may read this, these are some of the questions among others that you can potentially answer and should consider if and when you spot a fish kill. Obviously, another would be how many dead fish?…a count or numerical estimate. In a huge fish kill, a count per, let’s say, 100 ft of stream, river shoreline, or lake shoreline at a representative spot is better than no count, as this gives some idea of possible severity to investigators who are not yet on the scene.