corrosion on GPS plug

[tigerhead]

Sulphurboy,
How old is your GPS? I can't say for sure but I tend to doubt the corrosion is the reason you are seeing land where the water should be. If it's happening out in the middle the lake, you may be right, but I had a similar problem when I was near shore that I fixed by having Garmin update my software. You still need to deal with the corrosion so it doesn't ruin your unit, but call your manufacturer's service department and see what they say about the other issue.