Often the discussion on this messageboard is about how deep to fish under different conditions of time of year, water temperature and such. My question is, how does one know just how deep a plug, jig or other lure is running? This has always been a mystery to me. Experienced fishermen talk about fish at 6 to 12 feet but what determines that - the rate of retrieve or trolling speed, the angle of the spin on the front of a lure or what, and if you want to fish at 10 or 12 feet, how do you know when you have it right? I fish quite a bit but still do not know the answer to this, and I know it is important. Help!

Precision trolling sells charts for lure running depths. Or Just Google lure diving depths and many charts pop up.

Usually, when guys talk about the depth they were catching fish at, it is because they were watching their electronics. If they are talking about catching fish at 12 feet, they mean it was 12 feet deep where they were catching them. You can learn the trolling depths of specific lures from a few different places. Experience is the best guide, but sometimes, especially in deeper water, you need a line-counter reel and info on lures. There are apps for that as well as books.
If you are trolling in, say, ten feet of water, let out enough line that you are tapping bottom once in a while, but not too often. Then try to replicate it. Line counter reels are wonderful tools for this, other wise it is either a guessing game or you can feel the bottom.
It matters more for some species than others. Walleyes care, northerns less so.

The easiest way to tell is check your depthfinder and when your lure is out however far you have it find a depth that you hit bottom and then adjust accordingly. Different lures run to different depths at different speeds, with different amounts of line out. You could win a noble prize for if you could solve this quantum equation. So to be accurate as possible try to mark how much line you have out first, this can be done with a majic marker mark on your line, with a linecounter reel or just try to figure out some method so you can duplicate how much line is out so you can repeat it. Then try to choose a lure that will run approximately to the depth your looking at, so if your trying to get down 8 feet dont tie on a 25ft plus deep running crankbait. The last thing if possible is pay very close attention to your spped on your depthfinder if you have one, and try to duplicate that speed when trolling. If you dont have any of these things and its just you a canoe and a lure then cast it out and try to find bottom and then troll a little deeper.

Thank you. I appreciate these suggestions. Since I do not have a depth finder and will not bring along the charts or an app to tell me how deep a particular plug will run at the unknown speed with which I am retrieving or trolling it, I will have to take the most pragmatic approach available, which I gather is to bring some shallow and some deep runners and then try to let out line to find bottom without snagging up and losing the lure. Although I fish quite a lot, much of it is in the sea or flyfishing for trout mostly in NZ- both very different games from fishing northern lakes for walleyes or lakers. I clearly qualify as a rank amateur compared to you guys who responded. I will work on it. Thank you again for taking time to respond. I do love these messageboards. David

You can copy the dive charts and tape it to the inside of your tackle box.
Make sure your lure is tuned or the dive charts are worthless.