Iowa is one of those States that can definitely boast the four seasons. By the time January rolls around we are in a deep freeze with temps averaging in the mid-20’s to mid-30’s. Spring rolls around and things thaw out, temps rise and the rains come. Spring gives way to summer and things heat up. We’ve enjoyed the spring and early summer bit, and then August greets us full on…in a word…HOT!

Historically temps in Iowa run between 80 and 85 degrees on average. Heat indexes can push the temp to over 90 degrees and sometimes passing the century mark. Water temps follow and surface temps will reach into the 70’s. Increasing water temps will have a direct affect on your fishing…so let’s take a short lesson in science.

Like any living organism, fish that inhabit our local lakes, rivers and streams, need oxygen to survive. As water moves past their gills, microscopic bubbles of oxygen gas in the water called dissolved oxygen (DO) are transferred from the water to their blood.

As summer wears on three layers of water develop in Iowa lakes and reservoirs. The depth of these layers will depend on the depth of the lake. The top layer is called the epilimnion and gets the most sun and is the warmest of the three. The bottom layer is called hypolimnion which is least affected by sun and is the coldest. The middle layer is called the thermocline, a thin but distinct layer in a body of water.

The thermocline is of primary interest to anglers due to the fact that this is where the highest levels of DO will be found. The warm water at the surface will have DO but not at comfortable concentrations for fish and the water at the bottom of the lake will be too cold and the DO levels there will be very low due the lack of sun and the decomposition that usually occurs at those depths.

Here’s the first and maybe the most important tip when it comes to fishing the “cline”. Treat the thermocline like you would the bottom. “Anglers can often determine the thermocline on any given body of water using their depth finders”, said Iowa Department of Natural Resources Fisheries Management Biologist Ben Dodd. “Turn the sensitivity up and the thermocline typically appears as a horizontal line of debris.  Focus your efforts above that depth and you will increase your success.” You can also find historical data on the thermocline in Iowa lakes by going to

When it comes to fish and their summer time habits, giving consideration to the thermocline is a must. We’re going to take a look at some of our top quarry and break down a little bit about summer habits as well as some of the best baits to use.

Bass are one of my all-time favorite fish to chase after; especially for that early morning top water bite. I have often wondered if bass, like any other fish, tend to follow the thermocline. “Bass follow the rules of the thermocline as well”, said Dodd. “Bass tend to hang out in the shade (under docks and vegetation) or on secondary humps.” Best times to catch these fish are early morning and evening into dark. These fish are typically aggressive when they are feeding so fish aggressively with top water lures. One of the best top water baits and popular among many bass anglers is the Spook. It catches fish in all water conditions and in most bodies of water. The most important thing with the Spook is the walk-the-dog retrieve. It takes some practice, but once mastered it becomes second nature.

As the day warms up and the fish go deep, you can’t go wrong with Texas rigged worm or creature bait. I’ve had great success with these under docks and in vegetation. One afternoon as the sun was beating down on the water I found a tree branch reaching way out over the lake, shading about a 10 foot area beneath it. I knew there was a couple stumps down there, so I pitched my Texas rigged worm out and gave it a few twitches and BAM!, before I knew it a nice size bass had chomped on the bait. The look of disbelief on my partners face was worth making that cast into “nowhere”.

“We tend to find crappie and bluegill, especially the larger fish, suspended over the thermocline during the summer months”, said Dodd. “I prefer to drift with small pieces of crawler and yellow/orange jigs if I’m after bluegill. I use white/pink jigs and minnows for crappie. Crappies suspending in hot water can be agonizingly slow to bite. Using a drift rig, slowly drift over a school that you’ve marked with your electronics. Keep in mind that if it’s really warm and muggy that minnows will fade quickly in the heat. Switching to a tube jig or a tandem jig rig will improve your chances.

Weather will also have an effect on how these fish will react. Windy days you may find the fish more aggressive, since the turbid water increases oxygenation as well as bringing in windblown plankton for them to feed on. Slowly swim a small white or chartreuse twister jig along the channel where crappie may rise up from.

High pressure, which will affect any of the fish we talk about, will cause them to go deep and develop lock jaw. These fish still need to feed, so fish vertically over fish you’ve targeted with your electronics. A dropping pressure before a storm will make these fish active, aggressive and hungry. I keep a barometer close at hand and check to see whether I’m heading out on a rising or falling pressure change.

“Walleye in our impoundments tend to act quite similar to largemouth bass, believe it or not”, noted Dodd. “However, if flow is entering the lake from tributaries during and after storm events, walleye like to key in on those areas to increase feeding efficiency”. In early summer walleye movement is haphazard and random, you’ll likely find them all over the lake. As the water temperatures start to rise and aquatic vegetation emerges forming suitable protective cover, they will move in to these areas where they can lay in ambush. Walleye movement is reduced and they will establish smaller and more predictable activity centers.

“In the summer walleye will converge on the base or bottom portions of the weeds”, said Kevan Paul of Kevan Paul’s Guide Service. “The bottoms will stay cool enough and the fish will really key in on these areas.” You can target these areas with a slip bobber, vertical jigging or slow trolling spinners. Getting as close to the weeds as well as down towards the bottom will increase success.

“Typically I will fish leaches until they are no longer available, which is usually the case in August”, continued Paul. “I will go to a whole night crawler and will rig it “wacky” style, 2 or 3 times in the middle, on a 1/16oz jig and fish it vertically along deeper weedlines.” You can cast to these weedlines, but placing the jig in the exact spot where the fish can see the bait will certainly increase your chances of a hookup. Most of the weed beds that you’re looking for are submerged and will be seen on your electronics.

Early in the summer, catfish anglers will focus on large rip-rap and habitat since the fish will be spawning in cavities, this works for both catfish species. “Mid-summer, anglers can drift cut bait for channel catfish with success in most of our lakes”, continued the biologist. “Remember though, don’t fish below the thermocline!”

Saylorville Lake is a popular catfish fishing destination. A technique that works very well for this lake and one that I’ve used in recent years is drifting with cut bait. Saylorville is full of shad, and early in the evening these shad will school up rather shallow. A fishing partner of mine had a cast net and we loaded up on some of these bait fish for use throughout the night. Using a 3oz bullet weight, we rigged up for some nighttime drifting. The shad were thread on to 4/0 and 5/0 circle hooks and cast out behind the boat. I allowed the light breeze to push us along, effectively covering quite a bit of water. Each pass in our chosen fishing area yielded at least a bite or two. We ended our drifts when water depths approached 15 feet or so.
August fishing can be brutal at times, but with some planning and a bit of strategy, you can hit area lakes at the right time, using the right bait, and make the most of your fun in the sun…Tight Lines All!