Check to see what the map shows and compare it to what the sonar is showing, then make the necessary adjustments. You're making it more difficult than it needs to be.
Does anyone know what the lake levels are at when the lakes were surveyed? I know I can find out what current lake levels our from my local sources but when I go to offset the lake levels on my fish finder how do I do this accurately with out knowing what the lake was orginally surveyed at?
Check to see what the map shows and compare it to what the sonar is showing, then make the necessary adjustments. You're making it more difficult than it needs to be.
I do not know if you have an Hbird or Low depth finder, on Hbirds you can do a water offset ( in the menu ). Find a depth contour on your depth finder and follow it and note what your depth finder actually says, then make adjustments so the two correlate. Just remember if you go to a different lake to change it back to zero. Hibrd will do this with the GPS also if the lake coordinates are way off. Find a solid object bridge piling etc and reset the GPS.
According to LakeMaster: the lake levels are created according to the original water levels or full pool levels of the body of water. I had to ask what the difference in these two terms were and was told that full pool was used for reservoirs and original water levels was used for natural lakes.
So I guess that you could pull up the current water level where you are going to fish, make the offset in your Humminbird unit and see whether the spots that you thought wanted to fish even have water over them!