Help! Fish finder interpretation

[BearLakeFishGuy]

Those diagonal lines are mostly caused by the transducer not being perpendicular to the bottom. (There is a slight chance it could be fish ascending/descending in the water column quickly though). I've seen this many times on some hyrdoacoustic returns from survey-grade sonar (price about $50K) and once the transducer is adjusted, it will turn the fish into purdy little arches. Also, make sure the transducer is not only orientated to 90 degrees to the bottom/fish, but also orientated towards the direction you are traveling. If you have anything but an ice fishing style transducer (think: upside down ice cream cone in shape), this could also cause the arches to turn into "slash marks".