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Understanding Warmwater Fly Fishing Strategies

In the trout world, anglers probably all agree that a basic understanding of insects, fish behavior, and hydrology all help you catch fish. But many fly anglers lack that same knowledge for warm water fishing, often just throwing poppers or streamers with little understanding of the world beneath the surface. In this article, we’re going to take a dip into the ecology of warm water lakes. 

Difference between Coldwater and Warm Water Lakes

The primary difference between trout and bass lakes comes down to how much nutrient input a lake receives. Oligotrophic lakes, commonly associated with cold clear waters, are low in nutrients like nitrogen and phosphorus, while also being abundant in dissolved oxygen. Their counterpart, eutrophic lakes are most often associated with murkier water, high in nutrients like nitrogen and phosphorus, and may hold less available oxygen. You might think of eutrophic as a strictly negative term, like the Dead Zone in the Gulf of Mexico, where eutrophication is so bad that almost nothing besides tiny decomposing organisms can withstand the insane oxygen depletion. But a healthy eutrophic lake can support lots of life, including gamefish. These eutrophic lakes are where bass thrive. 

Warmwater Food Webs

Generally, eutrophic lakes are low elevation, shallow lakes. These characteristics coincide with warmer water due to ample light penetration, which also allows for abundant plant growth. You can easily identify these lakes by their greenish ting, caused by photosynthetic algae and phytoplankton. This algae lays the base for the food web that supports warmwater gamefish like bass. Algae provide the prey base for predatory zooplankton, and other microorganisms that feed on algae. Phytoplankton and zooplankton then act as food for macroinvertebrates, small baitfish and even juvenile gamefish. 

With so much growth at the lowest stages of the food chain, large populations of fish are easily supported in these lakes. Small baitfish, and juvenile gamefish have ample forage to grow larger, supporting recruitment for many juvenile gamefish to reach adulthood and reach greater sizes. Plus those that don’t make it to adulthood provide high-caloric-value prey for existing adult gamefish and apex predators. 

Ample nutrients and warmth from abundant sunlight also allow for rooted plants to take hold along shorelines, providing habitat for many lake dwelling species. Rooted plants may provide structure or shelter for phytoplankton or zooplankton. This draws in invertebrates to feed, mate, and also avoid predators. Soon to follow are small baitfish, searching for similar advantages, and not too long after the largest predators catch on to hunting in these areas. This in turn explains why predators gravitate towards these types of structure, the concentration of food around plants, shade, logs, each concentrating predator activity and should be the main focus of anglers targeting bass and other warmwater species. 

Caption: Food web showing the interactions of warmwater species in a typical warmwater lake (Agrilife, 2013)

Best Flies: Poppers and Streamers

To clarify, stillwater trout and smallmouth tactics operate similar in colder oligotrophic lakes (you want to target structure), but warm lakes offer a greater availability of prey due to their warm nutrient rich waters, supporting a more complex food web with higher value prey items thriving in greater density. In cold trout lakes there is simply less biomass available, so targeting trout requires use of flies mimicking bugs and small prey items in addition to baitfish, crayfish and leech patterns. Meanwhile in warmwater lakes, anglers need only to target those predators specialized in hunting prey with the highest caloric value. Just look at how wide a largemouth bass can open its mouth compared to a trout. They have evolved to chase bigger prey. Don’t hesitate to throw larger than expected flies at bass, they eagerly lean on poppers and large streamers. 

Within the food chain, as you climb to a higher level, from producer to consumer, about 90% of energy is lost (mostly as heat). Think about it this way, 100 pounds of insects, crayfish are needed to produce 10 pounds of bluegill, and that 10 pounds of bluegill would be necessary to produce a 1 pound largemouth bass. Interestingly, this ecological rule is generally widespread throughout nature, prey usually outnumber predators around 10-1. Large bass can’t wait around chasing smaller items, they just don’t provide enough energy. Then think about warm temperatures in these warmwater lakes, gamefish metabolism can ramp up earlier in the spring and stay active later into the fall (compared to a coldwater, high elevation lake), leaving hungry bass, pike, walleye, plus any other predatory warmwater species. 

Too Much Food Can Cause Problems

Even though warmer water can grow more fish, angler’s aren’t always guaranteed to find large fish. At times, too much food is available, causing an excess in juvenile fish able to survive into early adulthood. As a result, competition is greatly increased within this large cohort of similar sized fish, none able to outgrow their peers. This is referred to as stunting (or a stunted fish). If you come across a lake where most of the fish you’re catching are small and approximately the same size, you’ve probably found an afflicted lake. A trade-off exists between a lake with great density of fish, and a lake with trophy fish; some lakes may harbor fewer fish but those fish are able to grow large with little competition. 

Oxygen in Warm Lakes

Another side effect of abundant life in eutrophic lakes is the risk of depleting available dissolved oxygen. Outside of photosynthetic species, everything else in these lakes is constantly breathing, and consuming oxygen. Dissolved oxygen can only be replenished by surface aeration (wind or human installed pumps), or through plant and phytoplankton production. Usually this isn’t a problem, but as summer heat develops, air temperatures rise, water temperatures rise, the metabolism for any lake species increases, and so does the whole lake's demand for oxygen. Lakes often “stratify” in summer, a process where cold water sinks below the hot surface water, this prevents the oxygen in the water from mixing with itself, limiting the oxygen availability to the cooler deeper water. For anglers that can be bad news. When this happens, gamefish follow the oxygenated cooler water deep, making angling difficult unless you’re prepared to fish 20 feet deep or even deeper. Low oxygen concentrations can also develop over winter when ice puts a lid on a lake not allowing for new oxygen to enter the system. In dramatic cases this causes fish kills. 

Good luck!

Now that we know a little more about how these lakes function you can fish with full confidence on your next outing. If you’re just starting out, target any kind of structure or shade line you can find, and remember the warmer the temperatures, the faster you should move your flies.

Author Bio:

Andy Witt, scientist and angler obsessed with chasing and understanding all gamefish, writes on the intersection of science, conservation, and fly fishing for Due West Anglers, based out of Denver, CO.


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