Despite it seeming like the days of using maps is behind us, there is still a lot of value in being able to read one.
This remains ever so true for anglers.
The maps in focus here are depth maps.
Depth maps contain key information that allows a person to gauge the layout of a fishery.
This includes things like channels, ledges, points, shallow flats, and more.
Being able to read a depth map to gain an idea of the structural makeup of rivers and lakes gives you as an angler the advantage into being able to locate and target high percentage fishing spots.
Below we'll briefly give an intro on depth maps and end by highlighting some areas of interest to look for that tend to hold fish.
Intro to Depth Maps and Contour Lines
Depth maps are used to represent the geographic position of objects and terrain as well as their distance from the surface.
Just how a topographic (topo) map can be used to show changes in elevation when concerning land (national forest trails), people will use a depth map to show changes in water depth of rivers, lakes, bays, and the like.
This is accomplished by using contour lines.
Contour lines provide us with a measure of elevation, or depth when concerning water, of specific geographic areas.
It's important when reading a depth map to first understand how the contour lines are being used.
Where a topo map of a national forest may only provide contour lines for every 100 ft. of change in elevation, a depth map will generally provide a contour line for every 1 ft. of change in water depth.
Check out the picture below for an idea of how contour lines on a depth map are typically portrayed.
In visualizing the image, hopefully you see a shallow region of a fishery, perhaps a small flat (top right of image), that tapers into deeper water where there is a small 1 ft. mound that rises back up to 15 ft.
Once you have a good understanding of the elevation or depth intervals that contour lines on a map represent, you're ready to begin visualizing the actual area that the map is depicting.
For a real life example, check out the below picture of a main lake point to see how depth maps and contour lines help paint the picture of lake and river structures.
Notice the more spaced-out contour lines from the depth map (left) representing a shallow, gradual slope which can be seen on the Google Earth photo (right) vs the narrower contour lines further out from the point indicating a quicker drop into deeper water.
By applying the same thinking when scouting out new fishing spots you can soon begin to form an idea of the different regions of a lake or river that may be holding fish.
Below are some points of interest to be on the lookout for the next time you find yourself looking at a depth map of your fishery.
Points
A point is a piece of land that slopes into deeper water on three sides.
Most points can be easily identified by the layout of the land and nearby shoreline.
Points are often fished by bank anglers and boaters and are heavily sought after targets since tending to hold fish year-round.
For fishing purposes, it's advantageous to pay close attention to the contour lines around a point to know the difference between long, shallow running points and shorter, deeper points.
Channels
Channels are typically deeper areas of a body of water that contain more current.
Channels typically include a steep side and a shallow side.
This is nature's way of using current and water erosion to form cutbanks and points throughout lakes and rivers.
It can sometimes be advantageous for an angler to pay special attention to channel swings.
Channel swings are areas where a deeper cutbank begins to wash out into more gradual, depth changing areas.
The below picture highlights channel swing areas that can be seen where the contour lines begin to space out thus indicating a more gradual change from deep to shallow water.
It's not uncommon to find washed up fishing cover (submerged timber, etc.) around channel swings which make them great holding areas for both bass and baitfish.
Ledges
If you enjoy offshore fishing then you will love ledge fishing!
Ledges are any area that moves from shallow water to deep water within a relatively short distance.
Often found around channels, ledges typically make up the shallow-to-steep grade of a channel.
The above picture shows a steep ledge that transitions from relatively shallow water to deeper water along a creek bed.
Ledges can also be found in more remote, offshore locations where a lake or river channel splits (see below picture).
Offshore ledges are great places to catch a lot of fish since being isolated from the more popular shoreline areas that receive a lot of fishing pressure from other anglers.
Mounds/Humps
Mounds, or humps, are areas that typically rise up from the lake bottom to create a shallower circle or oval shaped region.
Mounds, in most cases, can be viewed as small underwater islands.
They are great for creating changes in fishery flow patterns which generally attracts both baitfish and predatory fish alike.
These are also great areas that give fish quick access to both shallow to deep water.
Mounds don't always appear as being super steep and some will tend to be more gradual.
Check out the below picture for another example.
The two humps shown above are located at the mouth of a creek that join a region of the main lake.
This area is special because of the humps being right out from the main lake point.
Finding areas like the one above that incorporate multiple lake and river structures into one area will more times than not end up producing a lot of bites for anglers.
Flats
Anywhere within a fishery that has a relatively flat area, usually spanning from just a few yards to a few miles, can be considered a flat.
More times than not these areas include some aquatic vegetation because of the region being shallow enough to allow for good sunlight penetration thus promoting plant growth.
Bass, along with other fish (bluegill, etc.), will typically use flats for spawning.
In Conclusion
There's a lot that goes into finding good fishing spots but having a solid understanding of depth maps and how to read contour lines can be a good starting place.
A good resource to get you started in identifying lake or river structures of your own fishery is fishermap.org.
Using the map, zoom in on your fishery and hopefully you will find Navionics depth mapping data already associated with it.
Every fishery will be structured differently which makes it important in being able to pick out the differences between one piece of structure vs the other and discovering what makes one spot so unique when compared to others.
In terms of structure, it's typically those places that have a small delta about them, such as a sharp bend in a ledge or a hump right off of a point, that are areas worth going back to time and time again.
Find those and you'll find the fish!
Time to go catch 'em!
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