Biological Benefits of Lake Drawdown

SEDIMENT ACCUMULATION: Man-made lakes trap sediment that otherwise move naturally through streams. Streams flowing into a lake will deposit sediments where they meet the lake. Over time, the stream/lake confluence and the upper end of the lake and coves will build-up with sediment and become shallower. This represents a net loss of water volume and, therefore, a reduction of adult fish habitat for the lake. If left unmaintained the upper lake area will fill-in and become a wetland. The accumulated sediment must be removed to maintain a viable resource.

ROOTED AQUATIC PLANTS: A common complaint from lakefront property owners and lake users involves the excess growth of aquatic plants (weeds) rooted in the lake bed in shallow water areas. The plants grow from the lake bottom where sunlight can penetrate to the lake bottom. The weeds can make swimming, fishing and boat access difficult in those areas. Aquatic plants are good for the fish and ecology of the lake, so it is desirable not to eradicate the plants completely by stocking grass carp or using chemical herbicides. During the winter lake drawdown, the lakebed in these shallow water areas will be exposed to the air and frozen, which kills the roots of the aquatic weeds. The occasional lake drawdown helps control aquatic weeds in unwanted areas and allows them to grow in deeper water areas and avoid less desirable aquatic weed control measures.

NUTRIENT CYCLING: Fertile water is necessary for good fishing in the Ozarks. Nutrients flow into the lakes from tributary streams. These nutrients that benefit the lake food chain are often buried in the sediments, as they accumulate in the lake and do not cycle in the lakes natural food-chain. By allowing the lakebed to dry, crack open and aerate during the lake draw-down, the nutrients are released from the sediments in the lakebed when the lake refills. This is similar to aerating your lawn along with using fertilizer – it helps your soil to breathe and cycle nutrients. If terrestrial weeds and grasses can be established in the exposed lakebed during a drawdown, the lake receives an even better boost in nutrients from the rotting grass and weeds that die when recovered with water. Seeding the exposed lakebed with something like winter ryegrass might help accomplish this nutrient release when the lake refills.

FISH POPULATION BALANCE AND GROWTH RATES: While the lake’s water level is lowered, the fish in the lake are more crowded. This makes it easier for the big fish to eat the little fish and, therefore, usually results in temporarily increased growth rates. This helps keep the fish populations balanced with the proper proportions of prey to predator fish.

For questions about the biological benefits of a lake draw-down, call Darrell Bowman, the Property Owners Association’s lake ecologist and fisheries manager at (479) 855-5068.