Are there any depth finders on the market that can be hooked up to hand held gps to show waypoints from the hand held . On the lake I live on the winter draw down is 40 to 60 vertical feet , and I would like to be able to go out in the winter and mark structure and its elevation so I can keep up with it as the water rises and falls. There is plenty of structure to fish but it's a pain to stay on it after dark. I don't care if it's color or not just if it has enough backlight to be seen after dark. The hand held I have is a Garmin Etrex.

Yep, you can do it this way----http://store.humminbird.com/products/322947/AS_HHGPS

The unit you hook it to has to be a GPS combo unit

The best way is to get the waypoints with your handheld, then load them to a Lowrance, Humminbird, or Garmin sonar/GPS unit.

If you think you can hook up a regular sonar unit to a GPS unit and have that function, you cannot.

Thank you for your answers. One more question. Could the hand held be used as the depth finder combo antenna for the gps?

Thank you for your answers. One more question. Could the hand held be used as the depth finder combo antenna for the gps?

I don't know all of what that connection allows, but it does make the handheld the GPS antenna. The unit itself has to be a sonar unit that is GPS capable. It doesn't make a chart plotter out of a track plotter though like the Humminbird 718 and 728. It also does not make the sonar unit a monitor (larger display) for the handheld unit.