may have been prop wash from other boats, actual trash in the water due to high water. That is a shoot thru transducer that is mounted in towards the rear of my boat, with epoxy. There shouldn't be interference, and I get readings up to 45mph. That was a channel with a lot of pre-spawn fish hanging out.

Are you sure that you aren't trying to out think the unit? Maybe there aren't as many fish as you think, under your transducer?