Trout catch reports in August are always low for the big UK reservoirs. In the cooler depths, even with a DI8, they are hard to find. Especially when the reservoirs are 30m deep. But we had some toys. 
We aimed to enjoy a sunny day drifting across the lake, talking rubbish and theorising why we were not catching.  We would also be watching FishTV on the Humminbird.
In Spain I had great success spotting fish in the depths. I was curious about how it would work for deep trout .

In the middle of nowhere, in 25m of water, how would you know that there is a ridge with baitfish below?

Tightening up the clamp for the makeshift transducer pole, I felt eyes burning into me. It may have been my own guilty conscience, but there was a good mixture of curiosity and judgment.
Traces arced across the screen in the 6 and 15m range as we zig zagged across the reservoir bowl. In one area an enormous bait cloud filled the screen screen. It too, started 10m down, and continued to about a metre from the bottom at 25m.
I swear I could make out a big pike sitting under the shoal. We worked around the shoal for a while and, but decided to explore further after only a single nibble. I would love to know what fish these were.
Next up was an underwater ridge that rose sharply from 25m to 10m. Along its edge, baitfish hovered. Long streak type traces suggested fast moving predators hunting them – trout.
Positioning upwind, drogue out, I sent a long cast out the side of the boat. I fed out the rest of the fly line and starting counting. The DI8 snaked down for 45-thousands. A few strips and boom, a very long, but skinny rainbow raced away before coming to the net.
With no more action, despite seeing movement we moved further afield. We needed a new TV show. 
Seven or eight sonar streaks appeared on the screen. Again deep between 10 to 20m down. They were rapidly moving up and down the water column. It was fascinating to observe this hunting behaviour. Perhaps perch, but I suspected trout.
Repeating the upwind, drogue and long countdown approach, I counted out thousands until my fly line arrowed down below me. Perhaps at 60 degrees angle.  The zonker was deep. A few very fast strips upwards and it got hit. Hard. It reminded me of deep sea jigging. This was not a typical 3lb stocky as it tore line off the reel. A very chunky brown popped into the net a few minutes later.
Strip, strip, strip and boom. Again, on the next drift, my rod almost ripped out of my hands. The backing knot ticked through the guides and disappeared into the blue depths. Three deep runs later an even bigger brown, its tail as large as my hand porpoised through the surface. We could not believe that this fish, a tail as wide as my hand, only weighed 6lb 12oz.
FishTV was entertaining. It also found fish in the middle of the lake in areas I would not have fished before. Cheating? Perhaps, but it shed a completely new light on the shady behaviour of deep trout. Perhaps it could lead to a ferox hunting char in the depths.