Because there are so many contributing factors to image quality, there are no absolutes in Acoustic Imaging. However, denser objects will smooth surfaces will generally produce the best images.

In most lakes and rivers, objects on the bottom attract fish. The most commonly found objects are standing trees, stumps, logs, large slabs or piles of rocks, a few small boats and sometimes man-made structures.  Submerged logs and fallen trees are usually obvious because of their horizontal orientation to the bottom and the multiple "acoustic shadows" caused by branches of the trees. Trees in lakes are often still standing vertically and cast very long "acoustic shadows". They can be a hazard to navigation but, most acoustic imaging equipments are not capable of making that determination alone (divers and / or other equipments may be needed to evaluate the level of hazard that a detected object presents). Logs and trees laying on the bottom will usually have a short acoustic shadow.
        A man-made structure of steel, concrete, wood, or fiberglass will usually produce a very good image (like the tunnel entrances in the image to the left). Characteristics of man-made objects include very straight edges or smooth curves not normally found in nature.