Liners to Prevent Water Loss in Nursery Ponds

While few fish pond owners would try to building rearing or feed-out ponds without a solid liner, these materials are also needed for nursery ponds. Unexpected water loss through the ground can result in water quality and temperature fluctuations that kill off large percentages of your fry stock or at least trigger illness due to stress. A fish-safe pond liner from BTL Liners controls water loss, maintains steady water quality, and allows for easy cleaning between rounds of fry to eliminate decomposition issues.

Controlling Seepage

Impermeable liners in particularly bring seepage rates down to the lowest possible amount. Unlined and naturally lined ponds can lose up to 20-30% of their water volume on a monthly basis. Even if that eliminates the need for water changes, it can destabilize the soil around the pond and result in a dangerous washout. Collapsing walls and edges kill fish fry due to stirred up sediment and physical smothering. To protect both your pond and your fry, keep water from soaking into the ground around it with a liner. Fish-safe liners can reduce seepage to 5% or less per month of the total volume, leading to stable and dry surrounding ground.

Better Control of Water Quality

Liners of all types preserve the water quality of the nursery pond by preventing minerals and chemicals from entering the pond through the soil. With a reduced need to add new water to keep the pond topped up, there’s also a lower chance of contaminants coming in through a river or well supply. However, clay and mud liners are hard to clean and therefore affect water quality in a negative way. Impermeable liners are a better choice, and BTL Liners has plenty of options like the AquaArmor. If treatment for a viral or fungal infection is necessary, a solid liner ensures the entire dosage circulates evenly rather than settling in the soil.

Flexible Membranes

Despite being smooth and easy to clean, flexible membranes still offer a more natural environment than a fiberglass tank or tub. Since the nursery pond is seeded with a solid or pelleted fertilizer prior to filling, there’s always a layer of natural material on the bottom when the fry are present. Bottom feeders can find their favorite foods and other fish species can escape from larger siblings when there’s a thin but healthy layer of organic muck at the bottom.

Clay and Mud Liners

Natural liners are widely recommended for raising ornamental fish like koi and goldfish, but these materials aren’t the best option for the fry stage of development. Thick layers of mud often trap too much oxygen and reduce DO rates overnight to the point where fry simply can’t breathe. These liners are also hard to maintain and make it tricky to tell if you’ve got all the sludge out between fry cycles. As you rake out leaves and uneaten fish food, you’re constantly at risk for breaking up the natural liner are starting a leak. Even when kept intact, these types of nursery pond liners lose far more water to seepage than impermeable materials like flexible geomembranes.


Some fish keepers assume that concrete is their own permanent option for lining a high-intensity nursery pond for fry rearing. However, concrete is actually far from the best choice for rearing ponds unless it’s paired with the right flexible liner. Concrete pond liners are expensive, need an extensive curing period to stop releasing byproducts that can hurt fish, and crack sooner than you think to form water-losing leaks. By installing a flexible liner before pouring any concrete in a nursery pond or raceway, you’ll trap leaks that form inevitably as the concrete cracks.

With this information, you should know exactly which liner material you want to use for your fish nursery ponds. All fish species thrive when paired with a fish-safe flexible liner, while only some species can handle the challenges created by concrete or naturally lined ponds. Explore the full range of BTL Liners products to find the right one for your project.

Liners by BTL

AquaArmor Pond Liner

The most versatile liner on the market today, AquaArmor maximizes protection from harmful UV rays, tear resistance and punctures that cause leaks. Simply the best liner on the market.

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