Thursday Tips: Find the Thermocline

B.A.SS. Elite Series pro Brian Snowden
with a late-summer largemouth from Table Rock.

By late summer, many lakes and reservoirs around the country have stratified. Oversimplified (to accommodate my own very limited understanding), a cooler layer forms on the bottom, with a warmer layer on top. In-between is a narrow middle ground known as the thermocline, and that layer generally offers the greatest interest to fishermen.

The bottom layer tends to get too low in dissolved oxygen for many sportfish and baitfish. while the top layer commonly gets to warm. Fish move in an out of any of the layers, but they spend the most time in the middle, where both dissolved oxygen levels and temperatures are moderated. Although not exactly a "best of both worlds," the middle layer does offer the "least bad of both worlds" through the hottest days of summer. Even fish that are tolerant of warm water spend quite a bit of time near the thermocline because it holds big concentrations of food.

In lakes that stratify, finding the thermocline with electronics typically isn't difficult. The most obvious clue is that much of the bait and many larger fish will concentrate in the same depth range. Beyond that clue, though, the layers themselves each have a little bit different appearance on most graphs, and the thermocline often is easy to recognize.

If you know what depth range is likely to hold the most fish, you only have to figure out where they are within that zone. That part depends largely on the target species. Stripers, walleyes, trout other species that roam open water often will be suspended over much deeper water and roaming quite a bit, so the key to finding them often is to locate schools of baitfish. Look for seagulls resting or circling in an area. Usually baitfish are nearby.

Cover-oriented species like bass and crappie often will relate to cover or structure at the depth of the thermocline, so if you figure out that zone is 20 to 22 feet, start looking at points, humps and channel edges that offer good structure within depth range. If you can find stumps, boulders or a brushpile atop structure in the key depth range, that's even better.

Whether you locate specific fish to target or search as you go by trolling or drifting, set your lines so that your baits stay at the thermocline or slightly above it. Most fish are more likely to move up than down to fish.

Finally, continue to watch our electronics for more clues as you fish, and take note of every detail any time a fish bites.