Winter Drawdown as a Management Tool for Ponds

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As summer turns to fall, now is a good time for pond managers to consider things that can improve the pond for the following year. One technique that can positively impact ponds larger than one acre is the winter drawdown.

A winter drawdown involves draining 2-3 feet of water from a pond in mid-November and allowing spring rains to refill the pond sometime in February. The goal is to expose 35-50% of the pond bottom, the shallow areas of the pond, to freezing and drying. The percentage of the pond exposed is only an approximation and will require adjustment due to pond topography and shape, and the amount of shallow water. Drawdowns are not recommended for ponds smaller than one acre, because it might leave insufficient water to support the fish population. A drawdown during warm months is also not recommended, as heat and low dissolved oxygen can excessively stress fish, likely killing them, and it may enhance the spread of marginal nuisance plant species (such as cattails, alligatorweed, rushes, and willows).

When aquatic plants (particularly submersed species growing in shallow areas) are exposed during a drawdown, exposure can cause plant death by desiccation to the leaves and stems, collapse of the vascular system, and root death from freezing and desiccation. Emergent and floating aquatic plants can sometimes be controlled with drawdowns, but this can be species dependent.

During the winter, water freezes into ice at 00 C (320 F), and floats to the top. The water below the ice remains at 1-40 C, and submersed aquatic plants are usually protected from freezing. While seeds are essentially immune to freezing and thawing, if bottom sediments are exposed to air during drawdowns, vegetative structures are susceptible to drying and freezing which can negatively impact plant growth when spring arrives.

The severity of the winter weather can affect the results of a winter drawdown. A mild winter, especially one with persistent precipitation, may not provide the freezing and/or drying required for plant destruction. Conversely, a cold winter with lots of snow might also lead to disappointing results. Snow is an excellent insulator, so exposed bottom sediments that are constantly covered by snow may not experience the low temperatures required to kill overwintering structures. High levels of groundwater seepage may also reduce or negate the destructive effects on target species by keeping the area moist and unfrozen. Ideally, the sediments should be exposed for at least 6-8 weeks, with temperatures below freezing (00 C/ 320 F) for two weeks or more.

A winter drawdown can also impact fish populations. If the pond is two acres and the level dropped three feet, it is likely that half the water volume has been removed, and the surface area reduced by at least 30%. An environmental change of this level can dramatically alter habitat availability, fish behavior, and predator-prey interaction. While a long-term water reduction can lead to undesirable changes in the fishery, short-term drawdowns can provide benefits that few other strategies can easily achieve.

During a drawdown, fish are forced into the deeper areas of the pond as the shallow areas are drained. During this period, fish are more concentrated and predation on small fish can increase substantially. This can be especially true for typical bass/bluegill ponds which often have limited deep habitat. A pond referred to as “bluegill-crowded” is one containing bass and an overly abundant population of small bluegill. When a drawdown is performed on a “bluegill-crowded” pond, a shift in the population dynamics often follows. The fishery tends to shift towards fewer individuals, with better condition and fitness. The bass have been given access to a larger number of bluegill to eat, and the surviving bluegill now have reduced competition for food and habitat. A healthier predator/prey balance, along with improvements to shallow habitat (reduction of excessive vegetation, for example), can result in far more satisfying fishing in both the short- and long-term life of the pond.

While the water levels are low and the shoreline is exposed, retaining walls and docks can be repaired, areas where the shoreline is eroded can be filled, and other improvements can be more easily accomplished. When bottom sediments are exposed during a drawdown, the peripheral pond soils get a chance to breathe. The exposed ground dries and contracts, and organic matter dries and oxidizes (composts) more quickly. Shallow areas can become slightly deeper the following season due to this compaction and oxidation, reducing light penetration to the pond bottom and potentially reducing some aquatic plant growth.

A winter drawdown is one tool in the pond manager’s toolbox. If the conditions are right, it can beneficially impact a pond. More detailed information can be found in FSA9628 Winter Drawdown for Aquatic Weed Control and Pond Management.