Still Water Advice

Found rising fish while checking a potential spot without a rod. There were a decent number of rising rainbows in both shallow and deep water but I couldn’t see what they were rising too. As you can see from the picture the water was very still. I have never fly fished anything like this and I don’t know where to start. If it helps this is in the south east on a clear lake. Would love any help on what to throw, how, where, etc