Wow! Sorry I missed the discussion yesterday folks, however; I still think it is air bubbles. Not a stream of them (which would show more as a tree trunk cp) but just one or two or two smaller groups. Air bubble rise at a constant rate and this is shown by the very linear shape of the angled sonar returns. Now I don’t know that all sizes of air bubbles rise at the same rate, so that could partially account for the two different angled sonar returns but also, though they appear to have originated from the same location; all we really know for sure is that both air bubbles were at the same distance from the transducer when they entered the sonar beam. It is obvious that this unit is using a very wide sonar beam, or that it has some very wide side lobes. The air bubbles could have started at different spots on the bottom of the lake and travelled upwards through different parts of the sonar beam and give the same result. If you look at the colors shown for both returns you see that they returned less sonar energy to begin with, than more, then less again, but one of them returned more sonar energy for a longer period of time versus the other. Perhaps it was more centered in the sonar beam as the boat passed over it and the other more off to one side? Those fish symbols could be from the air bubbles as they tend to follow the same pathway that the air bubbles took. That large arch is definitely from something that reflected a large amount of sonar and not what I would expect an air bubble to look like nor even a school of fish (it should have been filled in if it were multiple fish).