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Getting the Sonar Drop on Deep Water Fish

By: Mark Romanack

These images are not a simulation, but actual walleye as they mark with the help of Medium CHIRP sonar technology.

Here in the Great Lakes, very clear water typically adds up to fish that are most comfortable in the shadowy depths. It’s during the dog days of summer that smallmouth, walleye, bluegill, lake trout and a host of other species are most likely to be found not in the shallows, but in the deepest available water. While most anglers are intimidated by fishing deep water, modern sonar makes it far easier to find and catch fish that have gone to Davy Jone’s locker.


Traditional broad beam sonar works nicely for hunting up deep water smallmouth. When these fish are active and cruising along near bottom, broad beam sonar does a magnificent job of marking the locations of these fish. Where broad beam sonar starts to suffer is when fish are holding tight to bottom in areas that feature a lot of rocks and boulders. In these situations broad beam sonar has a difficult time separating fish from bottom.

No matter what species of fish you’re after, equipping your boat with modern sonar is the fast track to success.


The acronym CHIRP stands for Compressed High Intensity Radar Pulse. In layman terms CHIRP sonar is made up of multiple and varying sonar pings compared to traditional broad beam sonar that uses a single ping frequency. The multiple pings provides CHIRP the ability to deliver significantly better target separation than broad beam sonar.

CHIRP sonar is especially useful when targeting fish that want to be near bottom and also fish that are hiding among rocks, boulders and other cover. My Lowrance sonar units have three different levels of CHIRP sonar to pick from including Low, Medium and High CHIRP. For most freshwater fishing applications Medium CHIRP is the ideal setting.


While structure scan is often thought of as a means for hunting fish in shallow water, this unique sonar skill set can also be very useful in deep water situations. The advantage of structure scan is it allows the angler to see a wider percentage of the lake bottom, covering not just below the boat, but also to the left and right of the boat.

This wider foot print is useful in hunting for spots on the spot. When fish push deep in the summer they still prefer to hang out around obvious cover such as sunken logs, boulders and softball to basketball sized rocks. Structure scan does an excellent job of providing a detailed picture of these kinds of structure and also marking fish among the structure.

To those who are not super familiar with Structure Scan, fish mark as ghost images similar to grains of rice. Structure scan mounts best to fiberglass boats that have a step pad at the back of the boat. This allows the rather large structure scan transducer to be mounted as close as possible to the centerline of the boat and in front of the prop that would otherwise create turbulence.


Recently at Fishing 411 we have started using the Ghost electric motor and are finding great success using the Active Imaging Nosecone transducer. Mounted on the bow of the boat, this sonar option makes it possible to see in front and to both sides of the boat while hunting for fish. Because the transducer is in front of the boat it also delivers a perfectly clear image free of turbulence.

Active Imaging technology can be used with any type of boat, but this new sonar option is especially useful for aluminum boats that are not well adapted to mounting structure scan transducers at the back of the boat.

Lake trout are just one of the many species that are primarily found in deep water during the summer months. Modern sonar makes it much easier to find and also catch fish that have gone to Davy Jone’s Locker!


Perhaps the ultimate sonar for deep water fishing applications is something called Active Target. Active Target is real time sonar that requires a special transducer and also a routing box. The Lowrance Elite FS and also the Lowrance HDS Live units are comparable with Active Target.

This unique form of sonar features several modes including a “forward”, “down” and “scout” views that allow anglers to hunt for fish. The forward mode is perfect for locating fish out in front of the boat that ultimately become casting targets. The down mode comes into play for vertical jigging and the scout mode shows the largest picture with coverage left/right and front of the boat.

Active Target makes it possible to not only see super detailed three dimensional images of fish, you can also see your lure and how fish are reacting to the lure. Armed with this technology for the first time it’s possible to drop a bait down and see if fish are reacting positively to the presentation or ignoring it completely!

This real time sonar experience is addictive as it allows anglers to interact with the fish and judge the response of fish instantly. This sonar technology is so detailed it’s even possible to identify the species of the fish being marked by the shapes that appear on the screen!


The dog days of summer are the perfect time to experiment with sonar technology. When fish go deep they can’t hide from sonar and anglers who understand how to get the most from the various sonar technologies on the market.


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