Pond types: formal, natural, raised and indoor
Key facts: Koi ponds can be built in several distinct forms, including formal geometric pools, natural irregularly shaped designs, raised-wall ponds, traditional Japanese garden ponds and indoor tank systems, each with different construction and maintenance implications.[1][2]
Pond and water-garden design can range from simple to complex, and from formal geometric shapes to irregular, natural-looking layouts[1]. The Southern Regional Aquaculture Center similarly distinguishes irregularly shaped water gardens, which have a natural look, from geometric shapes, which appear more formal[2]. Terminology in this area overlaps: some sources use “ornamental pond,” “water garden” and “fish garden” interchangeably, though some keepers reserve “water garden” for plant-focused features without ornamental fish[1].Koi ponds are also described as a traditional feature of Japanese gardens, though many hobbyists elsewhere build special ponds with no attempt to suggest a natural landscape[3]. Indoor tank systems, meanwhile, are used both by commercial ornamental fish farms and by individual keepers, particularly for overwintering or quarantine purposes[4][5].Formal ponds
Formal designs use geometric shapes and straight lines, in contrast to irregular, natural-looking layouts[1]. The Southern Regional Aquaculture Center describes geometric water gardens as appearing more formal, compared with irregularly shaped ponds that have a natural look[2]. Regardless of shape, planners are advised to plan how pipes, filters, fountains, lights and heaters will be concealed, and how the pool will be drained, with a bottom slope of at least 1 percent recommended to aid drainage[1].Natural and irregular ponds
Irregularly shaped water gardens are described as having a natural look[2]. Wikipedia’s entry on water gardens notes that when aquatic flora and fauna are balanced, an aquatic ecosystem develops that supports sustainable water quality and clarity, with elements such as boulders, waterfalls and bankside planting helping integrate the feature with the surrounding landscape[7]. The Wikipedia entry on koi ponds similarly describes “natural Eco System” ponds, in which beneficial bacteria are introduced to help the pond reach a self-sustaining balance, after which frequent water changes are discouraged so as not to upset that balance[3]. Vertical sides are discouraged in pond construction generally, since they erode rapidly and allow detritus to build up on the bottom; tiered or sloping sides, with 2-3 tiers about 12 inches (30 cm) wide each, are recommended instead, both to move detritus toward the deepest point and to provide ledges for aquatic plants[1].Japanese garden ponds
Koi ponds or lakes are described as a traditional feature of Japanese gardens[3]. According to the Wikipedia entry on Japanese gardens, water is an important feature of many such gardens, alongside rocks and gravel, and traditional Japanese gardens can be categorized into tsukiyama (hill gardens), karesansui (dry gardens) and chaniwa (tea gardens)[6]. Japanese garden design favors asymmetry and concealment, with features such as buildings, bridges and plantings placed to be discovered gradually along a winding path rather than viewed all at once, and with borrowed scenery from outside the garden sometimes incorporated to make the space feel larger[6]. One documented example, a courtyard pond at Du Cane Court in London designed by landscape gardener Seyemon Kusumoto, is stocked with koi[6]. By contrast, many koi-keeping hobbyists today build special ponds in small spaces with no attempt to suggest a natural landscape feature, a more utilitarian approach distinct from traditional Japanese garden design[3].Raised and above-ground ponds
Water gardens can be built with varying proportions above and below ground level; those built at least two-thirds below ground level retain heat in cold weather and stay cooler in hot weather, according to the Southern Regional Aquaculture Center, while ponds built totally above ground may need to be drained during winter, with fish and plants moved indoors[2]. Pond depth also matters for winter survival: koi keepers commonly build ponds with sufficient depth — commonly 3 to 5 feet (0.9 to 1.5 m) — to prevent the pond from freezing completely, so koi can swim under an ice layer[3]. The dealer Kodama Koi Farm states that deeper ponds are generally better for winter survival, ideally around 5 feet (1.5 m), though some keepers manage with 3 feet (0.9 m)[5].Indoor ponds and tanks
Indoor tank systems are used in commercial ornamental fish production: facilities increasingly cultivate fish indoors using water-recirculation systems, which take advantage of modern husbandry and filtration technology and can minimize the escape of farmed fish and reduce water use compared with outdoor ponds[4]. Wikipedia’s entry on fish farming likewise notes that aquarium-trade fish are raised using either indoor tank systems or outdoor pond systems, and that indoor systems use treatments such as ultraviolet sterilization, ozonation and oxygen injection to maintain water quality while minimizing environmental drawbacks such as escapes and pollutant release[8].For biosecurity purposes, a publication from the Southern Regional Aquaculture Center notes that disinfection and isolation are generally more difficult to achieve for outdoor pond aquaculture than for indoor tank culture[9]. In home koi keeping, indoor holding tanks are also used seasonally: the dealer Kodama Koi Farm describes moving koi to a holding tank in an enclosed space, ideally with a heater, during winter hibernation, as a way to monitor fish that would otherwise be hidden beneath ice[5]. However, according to another dealer source, Kodama Koi Farm, koi generally live longer in a pond than in an aquarium, benefiting from more space, better water circulation and natural sunlight, and indoor koi kept in small tanks often have shorter lifespans[10].Construction and siting considerations
Across all pond types, siting and construction details affect long-term performance. Ponds should not be located directly under trees, because roots hamper excavation and may cause later structural damage, and overhanging branches can shed leaves and toxic substances into the water[2]. Sites should also avoid areas where the water table meets the depth of the main pool, and where surrounding land is higher than the pond, a berm can be used to deflect runoff[1][2]. Ponds deeper than about 18 inches (46 cm) may be considered an “attractive nuisance” by insurance companies in some jurisdictions and may need to be fenced, so checking with an insurance company before construction is advised[2]. Before installing a liner, the sides of an excavated area should be covered and packed with sand to protect against puncture from roots or rocks, and the pond should be filled gradually during construction to equalize pressure between liner and ground[1].Common questions
What is the difference between a formal and a natural koi pond?
Are raised ponds suitable for cold climates?
Ponds built mostly above ground may need to be drained in winter with fish and plants moved indoors, whereas ponds built at least two-thirds below ground level retain heat better in cold weather[2].
Is keeping koi indoors in a tank a good long-term option?
Are koi ponds always part of traditional Japanese garden design?
Koi ponds or lakes are described as a traditional feature of Japanese gardens, but many hobbyists today build ponds with no attempt to evoke a natural landscape, so the association is common but not universal[3].
Why do pond builders recommend sloped or tiered sides instead of vertical walls?
Vertical sides erode rapidly and allow detritus to build up on the bottom, so tiered or sloping sides are recommended to help move detritus toward the deepest part of the pool and to provide ledges for plants[1].
Related koi topics
References
- ^ Ornamental Fish Ponds and Water Gardens in Texas (Texas A&M AgriLife Extension). Texas A&M AgriLife Extension. extension.rwfm.tamu.edu/wp-content/uploads/sites/8/2013/09/Ornament…. Retrieved November 2026.
- ^ SRAC Publication No. 435: Water Gardens. Southern Regional Aquaculture Center. srac.msstate.edu/pdfs/Fact%20Sheets/435%20Water%20Gardens.pdf. Retrieved November 2026.
- ^ Koi pond (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Koi_pond. Retrieved November 2026.
- ^ UF/IFAS EDIS FA124: The Ornamental Fish Trade. University of Florida IFAS Extension (EDIS). ask.ifas.ufl.edu/publication/FA124. Retrieved November 2026.
- ^ Koi Pond in Winter: Best Tips for Winter Koi Pond Preparation. Kodama Koi Farm (koi dealer). kodamakoifarm.com/winter-koi-pond-preparation-survival/. Retrieved November 2026.
- ^ Japanese garden (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Japanese_garden. Retrieved November 2026.
- ^ Water garden (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Water_garden. Retrieved November 2026.
- ^ Fish farming (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Fish_farming. Retrieved November 2026.
- ^ SRAC Publication No. 4712: Biosecurity in Aquaculture, Part 3: Ponds. Southern Regional Aquaculture Center. srac.msstate.edu/pdfs/Fact%20Sheets/4712%20Biosecurity%20in%20Aquac…. Retrieved November 2026.
- ^ How Long Do Koi Fish Live? What is Lifespan & Growth?. Kodama Koi Farm (koi dealer). kodamakoifarm.com/how-long-do-koi-fish-live/. Retrieved November 2026.