There were some honest answers there... check if you are set on Meters instead of Feet. Check to be sure you are not in demo mode. It could be grass sub-surfece. Try setting your sensitivity to a mid-level, if it's set high. I ha mine set high when I first bought the boat and one spot was showing some sort of soft structure almost to surface in 25ft of water.... I reset the sensitivity and bang... cleared up the problem and I started marking good solid bottom and bottom structure very distinctly.