HDS Carbon 16 not reading depth accurately in about 5 feet or less

[toddmote]

Good evening,

I recently purchased a used rig and it has a Lowrance HDS Carbon 16 at the helm. The unit reads depth fine via the thru-hull transducer till I start moving into water that is 5 feet or less. Basically it will read accurately then once I get into that 5 feet or less range it starts reading 12-13 feet which is obviously incorrect. I can overlay my structure depth and it reads correctly in shallow water, and as I ease back into deeper water the two depth readings marry back up and will be within a few .10ths of each other until I move back into shallow water. Any ideas on what is causing the thru-hull to read incorrectly in shallow water? Thanks in advance for your time and input.

Thanks, Todd