Indeed you will just need to put in the time scouting the lake. A bathymetric bottom contour map will be a great help if one is available and will eliminate a substantial amount of fishless water. It sounds like its a big enough lake that maybe one exists. But whether that information exists or not, I strongly suggest that you carry a GPS with you every time you are on the lake and exploring or fishing. Every time you test for depth and bottom type be sure to set a waypoint identifying your information. Say the name is X Lake. A bottom check may return 9 feet. Set a waypoint name of X9. There is also a comments section on the Waypoint display that allows you to put a few notes in there, say "thick weed bed." Even if you encounter another 9 foot depth, you can continue to use the same WP name X9 by just adding a suffix to make the WP name -- X9a, X9b, etc. What you are doing is creating your own bottom contour map on your GPS topo map lake image. Having this info available from year to year without the need to duplicate previous effort because you didn't record it will put you on fish quicker and more often than starting all over. The naming system allows you to look at all the Waypoints showing on your topo map and make sense of them quickly and easily. Stick with a simple and logical naming system. Be sure to mark waypoints for each of your spearing and/or tip up fishing locations with a comment on how that area performed as a future reference.
Remember, you may end up a frequent "regular" visiting and fishing/spearing this lake so starting out with good records will reap rewards in the future.
