Ponds benefit from winter drawdowns, UAPB specialist says

Arkansas Game and Fish Commission hatchery trucks ran several days the week of Nov. 18, delivering catchable-size rainbow trout to Family and Community Fishing Ponds for winter. (Special to The Commercial/Arkansas Game and Fish Commission)
Arkansas Game and Fish Commission hatchery trucks ran several days the week of Nov. 18, delivering catchable-size rainbow trout to Family and Community Fishing Ponds for winter. (Special to The Commercial/Arkansas Game and Fish Commission)


Deliberately reducing pond water levels during winter can provide benefits in aquatic weed, fishery and shoreline management in certain situations, according to Scott Jones, small impoundment Extension specialist, Department of Aquaculture and Fisheries at the University of Arkansas at Pine Bluff.

"This practice involves draining 30-50% of the normal water volume from the pond in November and maintaining this lower level until about February," Jones said. "After February, natural rainfall and runoff can refill the pond back to full levels in time for spring fish spawning."

For ponds with built-in and functional drainage piping, the process is as simple as opening the drain and closing it when the desired reduction is achieved, he said. For ponds without functional drains, home-made siphon drains or rented trash pumps can be employed to reduce water levels.

"Plant types also matter when considering a winter drawdown for aquatic plant control," Jones said. "Emergent plants are those that are rooted in or at the edge of water, with most of the plant standing up above the surface of the water. Common examples include alligatorweed, water primrose, rushes and cattails. Many emergent plants can spread more during a drawdown as they are no longer limited by water depth blocking sunlight. Though, during this time they are also more easily accessed for herbicide application, cutting or removing with weed trimming tools or machines and excavation equipment."

Submersed plants are those that are rooted, or quasi-rooted, in the water and almost all of the plant stays below the water surface. These plants tend to be more susceptible to desiccation and freezing during winter drawdowns leading to lower abundance the following warm season. Common examples include the milfoils, fanwort, coontail and hydrilla, Jones said. Some species, like coontail and hydrilla, feature reproductive adaptations that help them endure exposure to desiccation and freezing, allowing them to persist and return healthy even after a drawdown.

"Other control measures, like grass carp, would be a more effective approach for these two species than a drawdown in most situations," he said. "Some rooted floating plants, like spatterdock and fragrant waterlilies (not to be confused with drawdown-resistant American lotus), are also susceptible to drawdowns."

A more comprehensive list of plants and their response to winter drawdowns is available in Extension publication FSA9628 Winter Drawdowns for Aquatic Weed Control and Pond Management.

Weather conditions during the drawdown have a significant impact on how well it controls aquatic plants, Jones said. Ideally, the pond will experience six to eight weeks of exposed drying with at least two weeks of sub-freezing temperatures. Moist soil from rainfall or groundwater seepage, or significant snowfall insulating the covered ground can reduce the efficacy of the drawdown.

"Drawdowns can benefit the fishery in exposing small forage fish to predation. Often, especially in weedy ponds, forage fish can hide indefinitely from predators along the shallows among the weeds," he said. "While seemingly good for the forage fish, it often results in very slow growth of the forage species and weaker performance of the predators as they cannot access the forage."

Performing a drawdown achieves two fishery benefits; 1) the predators feed more efficiently going into winter, which helps survival and can give them a nutritional boost for the following spawning season and 2) forage fish numbers can be thinned so that remaining forage grows larger faster from reduced competition which can also help forage spawning the following season.

"Much like properly pruning a flower bush, cutting grass or culling a herd, thinning fish from a pond often leads to growth and health benefits to those who remain," Jones said. "Bass-crowded ponds, those with very few forage fish and very abundant bass, may not see any fishery improvements from a drawdown. Bass harvest, forage stocking and possibly habitat work would be necessary to correct this situation before drawdowns would become beneficial to the fishery."

Drawdowns provide opportunities to deepen shorelines, repair docks and piers, install habitat, and do decorative shoreline-scaping such as installing rock edges, flowering shoreline plants and bulkheads, he said.

Shallow water is one of the primary factors promoting aquatic weed growth. While water is drawn down, excavation equipment can be employed to deepen the pond edges to reach at least 3 feet deep quickly and reshape shorelines to the generally preferred 3:1 slope.

"Be sure to seed and protect freshly worked soil to reduce erosion and promote rapid regrowth of grass appropriate for the season," he said. "If you are in an area prone to leaky soils, it may be unwise to perform this type of excavation without subsequent soil compaction as it may compromise the sealing layers of the pond basin and lead to significant leaking."

According to Jones, drawdowns are generally not recommended during summer in Arkansas.

"For one, we typically already have natural water level declines from increased evaporation and reduced rainfall/runoff during summer. We are also less certain when precipitation will return enough to refill depleted water supplies, compared to winter and spring rainfall patterns," he said. "Most importantly, water quality issues during summer often become more severe the shallower the pond gets."

Higher water temperatures and less surface area to interact with air movement contributes to lower dissolved oxygen concentrations, elevated stress on fish and conditions more suitable for potentially harmful algal blooms to thrive, Jones said. While many submersed plants exposed to extremely hot and dry conditions from summer drawdowns are killed and their regrowth suppressed, the risk to fish often outweighs the reward.

For more information about winter drawdowns, call Jones at (870) 575-8185 or email him at pondmanagement@uapb.edu.

Debbie Archer is an extension associate – communications at the University of Arkansas at Pine Bluff School of Agriculture, Fisheries and Human Sciences.


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