I'm getting better at using and understanding how my fishfinder works but locating creek channels is another story. If I'm reading my manual correctly my sonar picks up the highest section of land so how is it ever going to see into the channel? If the channel is 5ft across and 5ft deep for instance and its 20 feet down the beam is only going to pick up the top , right? hope this makes sense. The lake is over 30 years old so the creeks might be silted in and hard to locate. Also would the creeks be where there is water flowing into the lake or can these form by underwater currents?

The first thing you need is a good map of your lake Look on it for a point you definitely know its location where the creek channel swings in toward the bank find the channel and that should give you an idea of what your looking for

your depth finder does not read the top it reads the bottom depth and the gray line will tell you the type of bottom.Just remember what you see on the depth finder is behind you.Lowrances

web page has a good tutoriall on setting them up

Sam,

Creek channels are formed prior to the lake filling. Current will help keep them from silting, but it is erosion that causes the channels to form. You will be able to tell when you get over the channel, you will see the bottom drop off and then rise again on the other side. On old lakes you may not find much of a channel because of silt and time. Lowrance does have great tutorials for learning how to interpret you electronics.

Good luck

Try "Fishing Hot Spots" for a map of your area lake. http://www.fishinghotspots.com/fhsinet/

Also get a good chartplotter you can get plug-ins that often have the "Hot Spots" maps with GPS coordinates listed.

If you want to graph creek channels, run slowly across them watching the graph, not parallel to the channel, across.  Use fishing bouys as you slowly run across the channel and notice the drop, mark it,  Mark it on the other side where it starts to rise with another bouy.  Move up from your other two bouys, 10 yds or more, repeat this process a few times,    A map , Gps coordinate something has shown you there is a gut, ditch, creek channel, down there,   After you have laid a pattern of bouys, you will see in relation to how that part of the chanel is running.  When locating bends, i will lays as many as ten bouys out to study the bends in the creek.  If this is a Lake it should recieve an influx of water once in a while.   Study the creek channel coming in from dry land surrounding the area of the lake you are graphing,  Does it recieve lots of run off from rains,  some creek channel will silt in over the years,  but the creek will still show up because the lake bottom is also silting in.  There are days, my fishing is strictly with electronics,  truly understanding what is down there and how it relates to humps, roadbeds, stumps, old bridges and other contour and structure is keys in unlocking where fish move to on days when they where stacked in the bend of the creek,  knowing what is around that area is as important, like the fish suspending in the bend for two weeks straight due to cold fronts continually passing.   Then after 3 or 4 days of warm weather, the fish are gone,  knowing that 200 yds up the creek channel, the water comes up on the norhtside of the lake into a 100 flat is 2-4 deep and the fish are moving up shallow and sunning from about 10:30-2:00 and a rattle trap is prime for the taking.  These are the same migration routes that will be used in spring when they start to move shallow to spawn.  Knowing the north side will hold more fish in the winter than south banks is important,  North banks offer protection from blistering cold winds and offer warner water in the winter.  Knowing where the warmest water is located in the winter is key to finding active fish.  

Pretty good advice for a sip ;D!

Here's a pretty good video I got the other day that is helpful for learning about and how to use your sonar.  I think it is worth the price and you may want to check it out:

http://bazzclazz.com/Videos/Skills_Videos/Sonar/sonar.html