I'm in Jacksonville, FL and I have the above fish finder. When I'm fishing the larger lakes in Fla. such as Orange and Lochloosa near Gainesville, the screen shows an image of the body of water with good detail. However, when I'm on smaller lakes and ponds, the fish finder doesn't show the body of water at all.

Why is that and is there a fix that will enable me to see on the screen an image of the body of water I'm on?

Thanks.