Contour Lines! What They Are and How To Use Them!

Contour Lines! What They Are and How To Use Them!

Contour lines are usually on a map that shows valleys and hills on land, and the steepness of slopes underwater on a particular lake or river you are looking at. They will allow you to get an understanding of the lakes bottom without seeing it underwater. Contour lines will have the same depth from one point to another.

Contour lines that are close together on a chart usually mean that the bottom has a steep variation. And lines that are more spaced apart have bottoms with small gradual slopes.

Here is a diagram with contour lines and some examples on how they work.

  • Point A sits right on the 0 foot contour line. Since all points on this line have an elevation of 0 feet, the elevation of point A is zero.
  • Point B sits right on the 10 foot contour line. Since all points on this line have an elevation of 10 feet, the elevation of point B is 10 ft.
  • Point C does not sit directly on a contour line so we can’t determine the elevation precisely. We do know that point C is between the 10 and 20 foot contour lines so its elevation must be greater than 10 feet and less than 20 feet. Because point C is midway between these contour lines we can estimate the elevation is about 15 feet (Note this assumes that the slope is constant between the two contour lines. This may not necessarily be the case).
  • We are even less sure of the elevation of point D than point C. Point D is inside the 20 foot contour line indicating its elevation is above 20 feet. Its elevation has to be less than 30 feet because there is no 30 foot contour line shown. But how much less? There is no way to tell from the map. The elevation could be 21 feet, or it could be 29 feet. An eight foot difference in elevation doesn’t seem like much, but remember these numbers are just an example. If the contour lines were spaced at 100 foot intervals instead of 10 foot, the difference would be a more significant 80 feet.
  • Just as with point C above, we need to estimate the elevation of point E somewhere between the 0 foot and 10 foot contour lines it lies in between. Because this point is closer to the 10 foot line than the 0 foot line, we estimate an elevation closer to 10. In this case 8 ft. seems reasonable. Again this estimation makes the assumption of a constant slope between these two contour lines.


Now that you have overlooked the diagram and hopefully have a better understanding of a contour line here are some methods below that may help you increase your success when fishing.

Contour lines are an ideal instrument that anglers can utilize to their advantage when targeting multiple big fish species in big lakes or rivers. Contour lines can be found in all sorts of bodies of water, and understanding them can pay off with trophy fish. Finding the right contour line in the depth off water you want to fish in is important, and in today’s technological world, it’s not hard to find some good contour charts and information. Phone apps are a perfect example.

Although there are many ways to use contour lines while fishing I have found that they have been most successful to me while applying these two methods.

1. Ice fishing
Being in possesion of a map or gps that displays contours before or while you are ice fishing can be of great value to you. It will allow you to analyze the lake you are fishing quickly and put you right on the swimming lanes most fish will travel thus saving you time and energy drilling many holes and checking depths with your sonar units. Think like the fish and try to figure out the transition lanes they would use between different contour depths, and drill your holes over these areas and your catch ratio will improve. Best areas to apply these techniques are underwater shoals, reefs, camel humps and saddles. Why didn’t I mention points your probably thinking? Well that’s simple. Points are no brainers and usually will always hold some fish and are one of the easiest places to figure out when fishing. Remember the days when most of us fished blind with no sonar and we tried new lakes. What’s the most common thing we looked for? 90 percent of us would say a point. So you get the picture? Use contour lines to your advantage on the spots mentioned above and reap the rewards they have to offer. Especially on lakes like Nipissing and Simcoe.

2. Trolling
Trolling has got to be the best time when contour lines really become effective. There is nothing better than being able to look at your gps that marks these lines, and follow every little move and change they make. This is highly effective when fishing big water for walleye, pike, muskie, great lake salmon and trout. Whether it be trolling planner boards, dipsy divers, or just plain flat-lining crankbaits, use contour lines to your advantage the next time you are out.