BlogAugust 2017

What are hydrographic maps and how can you use them?

What are hydrographic maps and how can you use them?

By Andy Whitcomb

Aug 14, 2017

Hydrographic maps provide valuable information above and below water. Here is what you can find on these maps and how it relates to your fishing trip.

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Hydrographic maps are a valuable source of information both above and below water. Detail varies greatly but if a tackle store has a hydrographic chart or map of a lake you will be boating and fishing, pick one up and study it. 

Above water, these maps or nautical charts provide information such as the shoreline shape, and the location of boat ramps, coves, points, and any dam. A hydrographic map also will give scale. It is important to have a good idea just how far it is from Point A to Point B.  

But perhaps just as valuable is the information a hydrographic map can supply below water, in the form of contour lines. When learning how to read a lake map for fishing, make sure to pay attention to lines in the water that kind of trace the shore line. Widely spaced contour lines mean a gradual slope or similar depth. Closely spaced contour lines are locations of steeper slopes, ridges, or drop-offs.

Why is this important?

This information about the depth and how it changes can help you locate fish. Deeper sections will be a source of cooler water during the heat of summer and may remain weedless because of the lack of sunlight reaching the bottom. Large flat areas may be spawning areas in the spring. An area with a steep slope can be a source of upwelling or current movement which hungry fish know, often carries food. And you may be able to locate channels that can act as fish “highways” during some parts of the year as fish move to or from spawning areas.

Hydrographic maps will help you find underwater humps, rock piles, and other places where the bottom changes. These transition areas often attract fish. When you are renewing your fishing license, see if you can find any hydrographic maps of lakes or rivers in your area. It can help make the outing a success.

Andy Whitcomb
Andy Whitcomb
Andy is an outdoor writer ( and stressed-out Dad has contributed over 380 blogs to since 2011. Born in Florida, but raised on banks of Oklahoma farm ponds, he now chases pike, smallmouth bass, and steelhead in Pennsylvania. After earning a B.S. in Zoology from OSU, he worked in fish hatcheries and as a fisheries research technician at OSU, Iowa State, and Michigan State.