Humminbird LCR 3004 - Manual (Page 18)

LEARNING TO READ THE DISPLAY
The following illustrations show some typical display with bottom, structure, and target returns.
These should help you in interpreting the information being displayed on your LCR.
Surface clutter: The STC in your LCR will normally eliminate surface clutter, however, in some
water conditions or when going across the wake of a boat the surface clutter will appear as
shown above.