I have a garmin 76csx and the older lake map set "US Recreational lakes with fishing hotspots v5.0". It has decent detail but the contour interval is 10 ft. 5ft would be better. It does allow you to find secondary channels, and the navigational info (channel marks) are great when running the lake at night. The lake I fish most often has a lot of winding channels and you can get in trouble quick if you don't stay in the channel. Like jmac said it's nice to have the same maps on a pc where you can pick out likely looking bottom contours then transfer the waypoints to your handheld. I've made some custom maps of my farm for the garmin and want to try to make some of the lake if I can ever find the bottom contour data online. It'd be nice to make maps with a much finer contour, maybe 3 ft. That'd let you pick out finer ditches and drains that wouldn't show up with the 10ft contour interval.