Could just be Shad .... bigger ones since it's so late in the year .... and/or the elongated streaks could be moving fish and your slow speed. Images are usually more crisp and individual fish images more pronounced when going well over 1mph. You might also consider using the 800kHz range in that water depth, as it will give you a more detailed image.

I don't really know .... I'm just going on what I've experienced with my Lowrance DI unit.