Jeff at Navionics

Jeff, I just bought a 2008 Premium North chip. When I inserted it into my Lowrance 19c, some lakes come up with detail but most of them are just blue with nothing. One example is Lake Dubay in Marathon/Portage counties. I have the latest program update for my system according to the Lowrance web site. What am I doing wrong that I do not get better detail.
Thanks, tr