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Aquatic Habitat Plan-Reservoir Problems and Rehabiliation

Reservoir Problems

From the 1920s through the 1980s, nearly 145,000 acres of multi-purpose reservoirs were constructed in Nebraska, primarily for flood protection and irrigation. During this period, anglers could turn their backs on reservoirs where fishing had begun to decline and concentrate on new, highly productive waters. When major reservoir construction halted in the mid-1980s, a decline in the quality of fishing was inevitable.

Today, most Nebraska reservoirs are past their prime and aging rapidly. They are filling with sediment, their shorelines are eroding, and their water is becoming muddy. Many reservoirs are drastically drawn down in summer because of irrigation demands.

Those conditions not only reduce the number of fish, but community, said Don Gabelhouse, administrator of the Game and Parks Commission's Fisheries Division. "As a reservoir degrades, populations of fish species that live near shore and can be caught from the bank decline. Stocking more largemouth bass, bluegill, black crappie and northern pike accomplishes little if quiet, clear water with aquatic vegetation is being replaced by wind-swept, muddy water. Brush piles and tire reefs can never match the food production and overall habitat value of even a modest weedbed.

"Reservoirs in this second stage of existence are best suited for open-water fish, such as walleyes, white bass, wipers and white crappies. A boat is almost a necessity to consistently catch these open-water fish, and opportunities for bank fishing are drastically reduced. Thus, angler use declines as reservoirs age.

"Reservoirs were built with a calculated life expectancy. In advanced stages of aging, their fish communities consist of species that thrive in murky, shallow systems with low oxygen content, species like bullheads and carp. However, we cannot stand by and watch this occur. We need to 'turn back the clock' and rehabilitate our aging reservoirs."

On February 23, 1996, the Nebraska Legislature began the process of turning back the clock with the passage of a bill creating the nation's first state Aquatic Habitat Stamp. The stamp, to be purchased by most Nebraska anglers starting January 1, 1997, will be used to enhance and restore aquatic habitat in the state's waters. Revenue generated from stamp sales will be deposited in an Aquatic Habitat Fund, and before any money is spent, the Appropriations and Natural Resources committees of the 1997 Nebraska Legislature must approve a plan detailing anticipated expenditures.

But for the Aquatic Habitat Fund to be effective, both anglers and legislative committees must understand why Nebraska needs such a program, what kinds of projects will be undertaken, what benefits the environment, fish populations and anglers can expect when the work is completed, and which reservoirs and lakes will be improved throughout the next six years.

Reservoir Rehabilitation Techniques

1. Reservoir drawdown: Exposing sediment and letting it air dry allows earth moving equipment to remove sediment from the basin.

3. Fish removal: The decision to remove an existing fish community with rotenone, a fish toxicant, is made only when few sport fish are present and their salvage is not cost effective. The cost of renovation is much lower when the water volume is reduced through reservoir drawdown. When refilled, the reservoir will be stocked with desirable sport fish.

4. Excavation: When the reservoir basin dries, sediment is removed with earth moving equipment in a fashion that will create ledges, trenches and drop-offs. Irregularities in a reservoir's basin attract and concentrate fish. Deep reservoirs also are less subject to fish kills than shallow ones.

5. Island Construction: Sediment spoil can be used to rebuild shorelines and create islands. Shoreline erosion caused by wave action gradually enlarges reservoirs. However, the extra water created is shallow, it absorbs the power of crashing waves and supports few fish. By removing silt from areas close to shore and depositing it at the existing bank, deep, fish supporting water can be created within casting distance of the bank. Sediment spoil excavated from the basin also can be relocated in the basin as islands. Creating islands has the same effect as creating more shoreline; they increase the amount of water producing desirable shoreline species, such as large mouth bass, bluegill and black crappie. Islands must be stabilized with rock riprap to prevent erosion.

dike 6. Sediment and nutrient control dikes: Installed at the upper reaches of reservoirs to form marshes, dikes trap sediment and agricultural runoff as water enters the lake. Trapping sediment above the reservoir where it can be removed periodically keeps the water in the reservoir clearer than if sediment is allowed to accumulate in the basin or remain suspended. The importance of clear water cannot be overstated.

Anglers catch more fish from clear water, and more sport fish can be supported by a reservoir with clear water. Clear water produces more zooplankton than muddy water, and those microscopic animals are the food on which small fish live. Regardless of size and bag limits, a bass will never reach five pounds if zooplankton is not available when the fish is no more than an inch long.

Water clarity also affects the amount of vegetation a reservoir will support. Sunlight does not penetrate murky water, so rooted aquatic plants, the key to good habitat, cannot grow. Aquatic plants provide refuge for young game fish and bait fish, feeding areas for predators and shade from summer sun, but aquatic vegetation has an even greater value. The leaves and stems provide surfaces on which crustaceans, aquatic insects and other food organisms attach and grow, and the plants' process of photosynthesis replenishes the water's vital oxygen supply. Sediment/nutrient dikes also benefit terrestrial wildlife, including furbearers and waterfowl, by creating wetlands above and below the structures.

breakwater7. Offshore breakwaters: Built near erosion-prone shorelines in water four or five feet deep, these structures create quiet water near shore. Structures must be connected to the shore at intervals to exclude boats, and culverts must be included to allow fish passage. These structures are a better alternative for stabilizing eroding shorelines than simply dumping rock riprap. Aquatic vegetation should grow between the structures and the shore, allowing both shore-bound anglers and boat anglers access to productive fishing water. Jetties also can serve as spawning habitat for walleyes.

8. Jetties: At the mouths of large coves, rock breakwater piers can be built from opposing shorelines, extending toward one another so that the opening between them is just wide enough to allow boat passage. These structures reduce wave action and shoreline erosion in the cove and provide anglers access to deep water. They, too, can enhance spawning habitat for walleyes.

9. Increased water storage: Summer drawdowns in irrigation reservoirs flush fish and reduce the space and habitat available for fish. Stable water levels would increase the number of small fish that survive beyond their first year of life, increasing the number of catchable-size fish for the future.

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