Why is my pond losing water?

A pond that keeps dropping is usually losing water through the soil, around a pipe, or through the dam, not just to the sun. First work out whether the loss is more than normal, then find where it goes. The repair depends entirely on the location, and most real repairs are a job for a licensed excavation contractor or an engineer.

Some loss is normal

Every pond drops. Missouri's Department of Conservation puts it this way: "Throughout the course of a year, a pond’s water level (even those without a leak) will drop because of evaporation, seepage, and withdrawals for household use, livestock watering and irrigation".^[1] In a dry year, rain may not replace what evaporates.

Seepage alone is also normal at a low level. "Well-constructed ponds with good soil may lose one inch of water per month to seepage".^[1] So a pond that dips in August and recovers after a wet autumn is probably fine. One that keeps falling when you are not drawing from it, or that falls faster than neighbouring ponds in the same weather, deserves a closer look.

Signs of a real leak

The same agency says "the most recognizable signs of a leaking pond are rapid water level decreases or the water falling below the level expected with normal use".^[1] Look below the dam as well as in the pond. "Wet spots and aquatic vegetation (like cattails) below the dam may be good indicators of seepage through the dam or around the drainpipe".^[1] A soggy patch that stays wet in dry weather, new cattails at the toe of the dam, or muddy water running from the base are all worth photographing and measuring.

If the dam itself is wet, leave the repair to a professional. The agency says to contact the NRCS, an engineer or a qualified contractor when structural work on a pond is needed.^[1]

Why ponds leak

Most leaks trace back to one of a few causes.

The soil. Extension guidance says "soils should contain a minimum of 20 percent clay for good compaction, which prevents excess seepage".^[1] Sandy or gravelly basins let water through, and in rocky ground "seepage often occurs through cracks or fractures in the rock".^[1] Where the soil is coarse, "a blanket of less permeable material (high clay content) may be necessary to prevent excess seepage".^[1]

The dam and its pipes. "Trees and roots should be removed from the area of the dam to prevent seepage from root decay".^[1] Decayed roots leave channels. Pipes through a dam are another weak point, which is why the same guidance says "anti-seep collars should be installed on spillway and livestock watering pipes".^[1]

Animals. Muskrats and other burrowing animals can damage a pond's seal, and the guidance advises you to keep brush, debris and aquatic vegetation cleared away from the dam "to discourage animals from burrowing into the dam, which can cause leaks".^[1]

Drought. It surprises owners, but a falling pond can start a leak: "when rainfall is below normal and the water level falls, exposed soil can dry and crack, causing leaks in the clay blanket that protects the pond basin".^[1]

Why the repair depends on finding the spot

The agency warns that "sealing a leaky pond can be a costly endeavor unless you can identify the exact location of the leak".^[1] Fixing a basin leak or a dam leak are different jobs. Full reconstruction is the most reliable and the most expensive: "the pond must be drained, and the basin sealed, or the dam repaired".^[1]

Cheaper options exist if the leak location is known. Bentonite, a swelling clay, is one, but it has limits: "Bentonite will not stop the leak immediately",^[1] and it "will not swell in water containing large quantities of mineral salts or acids".^[1] Spreading a compacted clay blanket over the drained basin is another.^[1] A contractor who has built ponds can tell you which fits your soil, how much it should cost, and whether the pond is worth fixing. Our pond cost guide, how much it costs to build a pond in Virginia, explains the drivers that also apply to repair, and how a backyard pond is built shows what a sound basin and dam look like.

Permits and rules

Repairing a dam can raise the same questions as building one. DCR says "dams of specified height and impoundment capacity are regulated by the Virginia Department of Conservation and Recreation and are required to comply with the Virginia Dam Safety Act".^[2] Before any work that changes the dam, spillway, or ground around a stream, read whether you need a permit to build a pond in Virginia and ask your locality about land-disturbance rules.

What to document first

A few notes help a contractor quote accurately: the date, the water level or a photo against a fixed mark each week, any wet spots below the dam, recent rain, and anything you draw from the pond. Ask each bidder for a written quote that names where they believe the leak is, how they will confirm it, and what happens if the first fix does not hold.

When to call a licensed pro

For the repair. Virginia's Board for Contractors says that "if the work you are considering is valued at $1,000 or more, a valid Virginia Contractor’s License is required for the license category in which the contractor is to work".^[3] Under the Code of Virginia, a Class C licence covers a single contract over $1,000 but less than $30,000,^[4] and Class B covers $30,000 or more, but less than $150,000.^[4] Check the licence before you pay a deposit, and call an engineer or the NRCS first if the dam itself is wet or eroding.

Loclis lists licensed local businesses. Browse excavation services, read more excavation answers, or describe your leaking pond once and licensed excavation businesses will quote it.