Reservoirs are man made lakes constructed by damning up a stream. The flooded canyon or valley provides a widely varied habitat. Engineers design reservoirs to store the greatest amount of water for irrigation, flood control, or electricity production. Hence reservoirs are sited with depths in mind and are usually very deep in character. The dam’s height
approximates its maximum depth. The significance to the angler is that a great majority of a reservoir lies outside the productive shallow littoral zones. An optimistic angler may view such a reservoir as a place where all of that immense water concentrates its fish in its limited shallows.
New reservoirs are much more productive than old ones. The recent flooding of standing vegetation causes its organic decay to be released into the food chain. This enhanced situation provides a temporary boom-town for aquatic weeds, insects and fish. After a few years this organic matter is used up and the reservoir loses much of its food chain causing fisheries decline. Hence, new reservoirs are hot spots which inevitably fade.
A reservoir terrain conveys much to the structure of its fishery. Flooding vast expanses of shallows can create giant littoral zones. Although, a disadvantage is that these littoral zones are subject to reservoir draw downs which fluctuates its depths causing much of it to go dry during the late summer season. This seasonal fluctuation deteriorates the quality of its littoral zone and of its fishery.
Flood control reservoirs can be subject to much siltation deposited during the run off times. This can be detrimental to the fishery of such reservoirs. An example is Montana’s Ennis Lake which has silted up so severely that it now overheats the water released into the once great “Bear Trap Canyon” of the Madison River. Now August temperatures can soar to an excess of 70 F causing fish kills. This reservoir was initially a great trout producer but has disintegrated to the point of a very limited fishery which has also affected its outlet river.
Utah’s enhanced Strawberry/Soldier Creek reservoir offers a more stable fishery. Here many small streams that are relatively free of silt were damned to form one huge reservoir. Its terrain consists of shallow valleys when flooded became immense littoral zones and its elevation and temperatures are ideal for trout habitat. Biologists manage this reservoir by stocking and maintaining it as a prime fishery. Strawberry Reservoir is an example of one of the better reservoirs.
The huge Colorado and Green River impoundments had their hay-days when they were young. Flaming Gorge Reservoir was a trophy brown and rainbow trout fishery in its early days; now it primarily a lake trout and small mouth bass fishery. Lake Powell has changed from a fantastic large mouth bass and crappie fishery to a stripped bass one. There are still fish to be caught in these older reservoirs but it takes some knowledge of where and how to fish them. In their youth, little skill was needed to catch fish.
The key to reservoir fishing is to search out the productive areas such as: inlets, channels, drop-offs, weed beds, shallows, shoals, cliffs and land points. Using accurate topographic maps of prior flooded real estate facilitates the location of these structures. The huge sizes of these reservoirs can easily conceal productive areas. A boat with a quality video sonar and time spent prospecting are assets to productive reservoir fishing.
Large portions of a reservoir harbor few or no fish. All of the fish are found concentrated into the few prime areas. Find these places and spend your time productively fishing them and not wasting your time in the fish poor areas.
Reservoirs stratify into the epilimnion, thermocline, and hypolimnion areas during the warm months of the year. Since reservoirs tend to be deep the hyolimnion area can be vast. The epilimnion is where light penetrates causing submerged weed growth that is the productive portion of a reservoir. It also generates the dissolved oxygen needed to sustain life. The
thermocline is the transitional zone with a drastic drop in water temperature which separates the epilimnion and hypolimnoin layers. The oxygen and food supply is limited to the eplilimnion and somewhat in the thermocline layers. The hypolimnion is usually depleted of food and oxygen making it unproductive. Learn to detect areas where the epilimnion and the thermocline correspond to the lakes bottom. Spend your time fishing these waters and eliminate the hypolimnion area altogether. A thermister with an oxygen monitor is useful in locating these layers. Next use your video sonar to find structured areas which fall into the desired epilimnion and thermocline areas.
During very warm weather the epilimnoin may become too warm to hold adequate oxygen for fish to sustain themselves. Fish will seek the thermocline where its cooler waters can hold more oxygen. Remember at this time the hypolimnion is cold but oxygen poor. Moreover the lakes entire fish population can be concentrated into this limited area. Locate bottom structure at the same depth of the thermocline and the fishing can be amazing.
Lake zones are also classified as to littoral, pelagic, and profundal zones; this classification is based according to light penetration and plant growth. The littoral zone is where photosynthesis occurs and concentrates the lakes food chain. The profundal zone is the deepest portion of a lake where photosynthesis and plant growth is severely limited; it is where little light penetrates. This profundal zone supports few fish and deep reservoirs harbors vast acreage of this zone. The pelagic zone is the top portion of the profundal zone and this pelagic zone is bordered on its sides by the littoral zones. Penetrating sunlight reaches here and oxygen is high but its bottom is only accessed by going through the dead profundal zone. Its importance is where the pelagic zone borders with the littoral zone because it is here that fish can gather hiding in this zone fish venture out into the shallows to ambush prey.
Junctional habitat seems to consistently concentrate animals; big game species such as elk and deer prefer areas adjacent to both open and forested areas. Elk feed in the open park grasses during low light conditions and migrate to hide in the forest cover during the day. Fish likewise use the pelagic zone as a darkened hideaway safe from predators and concealed from their prey. Surprise attacks on schooled minnows are initiated from this pelagic zone. A reservoir’s largest fish commonly behave in this manner by ambushing their prey at this littoral/pelagic zone junction.
These three zones of littoral, profundal, and pelagic do not change. It is the epilimnion, thermocline, and hypolimnion layers that are subject to changes due to weather conditions such as temperature changes and wind/wave actions.
When selecting a reservoir to fish take into account its anatomical features. Choose one with the most fish producing habitat. Look for one with an abundant littoral zone which has lots of weed beds, shoals, drop-offs, islands, peninsulas, inlets, cliffs, rocky and gravel areas within this zone. Fish these structures adjacent to the pelagic zone which provides both deeper cooler waters and darkened cover to conceal fish.
When fishing reservoirs with limited littoral zones
look for areas with structures located within these zones. The few good areas these reservoirs possess may have gone under-fished; furthermore these structured areas may provide a seldom fished hot spot.
Idaho’s failed Teton Dam Reservoir is rarely fished because it was a disaster site. Now its limited backed up pool contains some of the best trophy cutthroat fishing anywhere. This pool is all prime trout habitat. Every time I’ve ventured there I’m alone with its abundant trout and rattlesnakes; it has given up cutthroat to nine pounds.
In summary, reservoirs are difficult to locate their prime fish habitat because the vast amounts of stored water conceal them. Discover a reservoirs features and its fish may be concentrated there. Perhaps you can discover a reservoirs’ 10% that holds all of its fish. Identify these places and spend your time angling there.
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