I was up last week.  Usually I check the report with Mountain Hardware in Truckee:                                                                              ( http://www.mountainhardwareandsports.com/fishing-report  )   Before going up I also read a Truckee guides report saying that he was getting off the river before noon.

They were discouraging people from fishing after 11:00 because water temperatures were high and fish that were caught were being stressed.   In the evening I went out to fish the Little Truckee, but decided to check out Hershdale first.  There had been some thunder showers and the daytime temperatures were down.  Anyway, there were a number of people at Hershdale,  so I decided to go down and check out the canyon.  The water seemed to be higher then when I drove up last month so I fished it.  Caught three small ones on midges in my favorite hole and then moved downstream to another hole I like.  Got a couple of grabs close to where I was wading, and then shot a couple of casts across to the far side.  Hooked the biggest fish I've seen in ten years in the canyon.  Anyway, he made a run down into the rapids and one quick jump before taking my dropper.  He left me stressed.   Risk vs. reward.  I used midges on light tippet material to get grabs, but was in no position to work a big fish.

But to answer your question the water may have been a little on the warm side and the fish are less active in the day then at night and during the early morning hours.  Because I was further down the river I was picking up the water coming out of Stampede and Boca which was a little cooler.