01 Nov 5 Aquatic Plants That Clean Your Pond Water
Water lilies, water hyacinth, watercress, anacharis, and pickerel plants can reduce excess nutrients and algae, but they work best with proper filtration and maintenance.
By Shawn Schroeder
After more than 20 years servicing koi ponds, I have found that healthy plant life can make a noticeable difference in water quality when it is chosen and managed correctly. The right aquatic plants absorb nutrients, compete with algae, provide shade and cover for koi, and become part of the biological processes that keep a pond balanced.
Plants, however, are one component of a healthy koi pond. They cannot compensate for excessive fish waste, overfeeding, undersized filtration, poor circulation, or neglected maintenance. The goal is to combine plant-based nutrient uptake with effective filtration, proper fish management, and routine attention to water chemistry.
How Do Aquatic Plants Help Clean Pond Water?
Aquatic plants help clean pond water primarily by taking up nutrients that would otherwise be available to algae and other unwanted growth. Nitrogen and phosphorus enter a koi pond through fish waste, uneaten food, decaying leaves, fertilizer runoff, and other organic matter.
Those nutrients are not automatically bad. They are part of a functioning ecosystem. Problems begin when nutrients accumulate faster than the pond's biological system, plants, and filtration equipment can process them.
Oklahoma State University Extension describes aquatic plants as effective nutrient absorbers and filters and notes that submerged plants can help filter and oxygenate water. The same guidance explains that floating plants absorb nutrients directly through roots suspended in the water.
Plants also control algae indirectly. Algae needs nutrients and light, so a pond with healthy plant growth can reduce two resources algae depends on. Clemson Cooperative Extension identifies excess nutrients and sunlight as major causes of algae problems in water gardens.
There is an important limit to this approach. Too much vegetation can create its own water-quality problems. Dense plant growth can interfere with circulation, trap organic debris, consume oxygen at night, and eventually return nutrients to the water when old foliage decomposes.
1. Water Lilies
Water lilies help maintain clearer water by absorbing nutrients and shading the pond surface, which limits the sunlight available to algae.
In my experience, that combination makes lilies one of the most useful plants in an ornamental koi pond. Their large floating leaves create significant shade while their roots and growing tissues use nutrients from the pond environment.
William & Mary's Department of Biology specifically notes that water lilies absorb nutrients and can create enough shade to reduce algae growth. Utah State University Extension likewise identifies shade, fish protection, cleaner water, and aeration among the benefits plants can provide in ponds.
Shade is particularly valuable in Southern California. A pond exposed to strong Los Angeles sun can receive many hours of intense light every day, providing algae with an excellent growing environment when dissolved nutrients are also abundant.
That does not mean you should cover the entire pond with lily pads. Excessive surface coverage can interfere with gas exchange and reduce light to submerged vegetation. Penn State Extension warns that a pond completely covered by water lilies can become heavily shaded and biologically unbalanced.
I prefer to treat lilies as one part of the overall planting plan, with enough open water remaining for circulation, feeding, observation of the koi, and gas exchange.
Koi may also disturb pots or damage tender growth. Proper placement and protection of the root zone are therefore important when incorporating lilies into an established koi pond.
2. Water Hyacinth
Water hyacinth can remove dissolved nutrients very efficiently because its long, fibrous roots hang directly in the water column, giving the plant continuous access to nutrients carried past the roots.
Floating plants are especially useful from a water-treatment standpoint because their roots do not have to depend entirely on nutrients stored in soil. Illinois Extension explains that floating plants filter nutrients from pond water that might otherwise support algae, while their foliage shades the water and further limits algae growth.
Water hyacinth can therefore provide several useful functions at once: nutrient uptake, surface shade, fish shelter, and an extensive underwater root structure.
There is a major California-specific caution, however. Water hyacinth is an invasive, non-native aquatic plant in the state. California State Parks actively controls it in the Sacramento-San Joaquin Delta because uncontrolled plants can form dense mats, displace other vegetation, interfere with waterways, and damage aquatic ecosystems.
For a Los Angeles County koi pond, water hyacinth should therefore never be allowed to escape into a storm drain, creek, lake, river, wetland, or other natural waterway. Removed plants and fragments need to be disposed of responsibly rather than released.
It also grows quickly in favorable conditions. That means thinning is part of the job. Allowing an entire pond surface to become covered defeats the purpose of creating a balanced koi environment.
3. Watercress
Watercress can contribute to nutrient control when its roots have consistent access to nutrient-rich pond water, especially along shallow edges, streams, waterfalls, or planted filtration areas.
Watercress is a bog-type plant in pond applications. Our own plant guidance includes it among plants suited to wet pond margins. Utah State University Extension describes watercress as an aquatic plant that grows particularly well in shallow moving water with its roots submerged.
That growth habit makes watercress useful around pond streams and shallow biological areas where water is constantly passing through the roots.
The important concept is nutrient export. The plant incorporates nutrients into new stems and leaves as it grows. When excess growth is trimmed and physically removed from the system, some of those nutrients leave with it.
If overgrown material is simply allowed to die and decompose in the pond, much of the stored organic material eventually goes back into the water. Regular trimming therefore matters.
Watercress also needs to be kept under control. I do not recommend allowing any fast-growing plant to choke a waterfall, restrict a skimmer opening, cover a return line, or trap large amounts of sediment.
In a professionally designed pond, I often think of watercress as a useful polishing plant rather than the primary filtration system.
4. Anacharis
Anacharis is a submerged plant that can absorb nutrients from the aquatic environment while adding underwater plant structure to the pond.
Oklahoma State University Extension identifies anacharis among submerged plants that multiply rapidly while filtering and oxygenating water. It recommends submerged plants in areas where water movement allows them to participate effectively in the pond ecosystem.
Unlike lilies, anacharis performs most of its growth below the water surface. That gives it a different role in the planting plan. It competes for available nutrients without depending on large floating leaves for its primary benefit.
People commonly call plants like anacharis "oxygenators," but that term needs some qualification. Photosynthesis releases oxygen during periods of sufficient light, while plants also respire and consume oxygen, particularly at night.
A dense mass of submerged vegetation should therefore never be viewed as a substitute for aeration. The University of Florida notes that dense Egeria densa growth can contribute to low early-morning oxygen levels because the plants respire at night.
There is another important consideration for Southern California pond owners. The plant commonly sold under the name anacharis may be Egeria densa, or Brazilian waterweed. California considers Egeria densa an invasive submerged aquatic plant and conducts extensive control efforts against it in the Delta.
Do not release anacharis, plant fragments, or pond water containing fragments into natural waterways or drainage systems. Because fragments can establish new growth, containment and responsible disposal are especially important.
When I select submerged water plants for a koi pond, I consider their ecological status, the pond's construction, fish load, circulation, maintenance needs, and the likelihood that the koi will disturb them.
5. Pickerel Plant
Pickerel plant helps improve water quality by taking up nutrients through its root system while stabilizing planted margins and adding dense emergent growth at the pond's edge.
Also called pickerelweed, Pontederia cordata is an emergent or bog-type plant rather than a free-floating plant. Its roots remain wet or submerged while its leaves and purple flower spikes grow above the surface.
A University of Central Florida study examining floating treatment wetlands documented nutrient uptake and assimilation by pickerelweed as part of the system's nitrogen and phosphorus cycling. University of Florida guidance also identifies pickerelweed as useful for nutrient uptake and reduced turbidity in water-management applications.
In a koi pond, I like marginal plants such as pickerel because they can add considerable plant mass without covering the entire water surface. They are particularly useful where the pond design provides shelves, bog areas, or planted margins.
That does not make them maintenance-free. Pickerel can spread and should be pruned when necessary. Old foliage should also be removed before large amounts of dead plant material fall into the pond and begin decomposing.
Well-managed pickerel gives you the benefit of an active root zone while keeping much of the foliage above the water, where trimming and maintenance are relatively straightforward.
Which Plant Is Best for a Koi Pond?
The best approach is usually a combination of plant types rather than relying on one species to perform every job.
Water lilies are especially useful for surface shade. Marginal plants such as pickerel and watercress place active roots around shallow zones. Submerged plants can compete for nutrients below the surface, while carefully managed floating plants can draw nutrients directly from the water column.
Every pond is different, however. A lightly stocked ornamental pond and a heavily stocked koi pond can have dramatically different nutrient loads even if their dimensions are identical.
Fish size matters too. Several large koi can produce considerably more waste than a small group of juvenile fish. Feeding practices, sunlight exposure, water volume, circulation, filter capacity, debris load, and existing plant coverage all affect the amount and type of vegetation I would recommend.
Koi themselves also complicate plant selection because they may uproot, eat, or damage vegetation. Oklahoma State University Extension recommends protecting plants from koi when necessary.
The right planting plan has to work with the fish rather than simply look good on the day it is installed.
Can Plants Replace a Koi Pond Filter?
No. Plants can complement a filtration system, but they should not be treated as a replacement for properly sized mechanical and biological filtration in a koi pond.
Mechanical filtration physically captures suspended solids and debris. Biological filtration provides surfaces where beneficial microorganisms participate in processing dissolved waste compounds. Plants then provide another route for nutrient uptake.
At Aquatic Gardens, we consider pond size, fish load, environmental conditions, and the existing system when evaluating filtration. A quality filter helps remove debris, toxins, and excess nutrients and contributes directly to better water clarity and water quality.
A UV system may provide another layer of control when suspended algae is causing green water. UV filtration exposes microorganisms passing through the unit to ultraviolet radiation and can significantly reduce suspended algae and certain bacteria, but it does not eliminate the need for filter cleaning, debris removal, water testing, or other maintenance.
I see the best results when these systems work together: mechanical filtration removes solids, biological filtration supports waste processing, plants capture available nutrients, proper circulation moves water through the system, and routine maintenance prevents waste from accumulating faster than the ecosystem can handle it.
Why Can Too Many Pond Plants Cause Problems?
Too many plants can reduce circulation, trap debris, interfere with gas exchange, consume oxygen at night, and create a large amount of decaying organic matter.
Plant growth needs to be managed just like fish population and feeding.
One common mistake I see is assuming that if plants remove nutrients, twice as many plants must be twice as good. Pond biology is more complicated than that.
When vegetation becomes excessively dense, water can stagnate within plant masses. Dead roots and leaves accumulate. Filters and skimmers become blocked. Large amounts of decomposing plant material then consume oxygen and return nutrients to the system.
Penn State Extension warns that excessive surface vegetation can block light and interfere with oxygenation.
This is one reason seasonal thinning is so important. Our plant-care recommendations include thinning and spacing overgrown plants in spring and removing dead foliage during the growing season.
The objective is healthy, actively growing vegetation, not maximum vegetation.
What Else Keeps Koi Pond Water Clear?
Clear, healthy pond water depends on controlling the complete nutrient cycle, including feeding, fish waste, organic debris, filtration, plant growth, circulation, and maintenance.
Overfeeding is one of the first things I check when a koi pond continually struggles with algae. Uneaten food and increased fish waste put additional nutrients into the water, which can encourage algae and increase the workload placed on both plants and filtration equipment. Our koi pond maintenance guidance recommends feeding only an amount the fish can consume quickly rather than allowing excess food to remain in the system.
Routine removal of leaves, sludge, dying vegetation, and accumulated debris is equally important. Organic material that stays in the pond eventually decomposes, placing additional demand on oxygen and biological filtration.
Persistent algae can also be an indication that the pond needs more than additional plants. Filter performance, circulation, fish load, UV operation, feeding habits, debris accumulation, and water chemistry may all need to be evaluated.
For the ponds we service throughout Los Angeles and the San Fernando Valley, I look at the pond as a complete biological and mechanical system. Treating one symptom without finding the source usually leads to the same problem returning.
Creating a Cleaner, Healthier Pond With Plants
Water lilies, water hyacinth, watercress, anacharis, and pickerel plants can all contribute to cleaner pond water, but they accomplish that job in different ways. Some provide shade, some place nutrient-absorbing roots directly in the water, and others grow below the surface or along nutrient-rich pond margins.
The most important part is balance. Plants need to be compatible with the koi, filtration system, pond construction, maintenance schedule, and local environmental requirements. Fast-growing or invasive species also require particularly responsible containment and disposal.
Since starting Aquatic Gardens in 1999, I have worked with ponds throughout Los Angeles and the San Fernando Valley, including West Hollywood, Beverly Hills, Santa Monica, Malibu, Calabasas, Woodland Hills, Northridge, Simi Valley, and Camarillo. We provide plant selection and installation as part of a complete approach to koi health, filtration, water chemistry, and long-term pond care.
If you want plants that improve your pond's appearance while supporting better water quality, Aquatic Gardens can help you choose and install the right aquatic plants for your koi pond and maintain them as part of a balanced pond ecosystem.
About the Author
Shawn Schroeder is the founder and owner of Aquatic Gardens. He is a pond service technician with over 20 years of experience in the business. Shawn has extensive experience in koi health, aquatic plant care, pond filtration, and the chemical and biological compounds of pond water. For Shawn pond service is not just a business, but a passion as well. Shawn has taken a great interest in all fish; koi in particular, and pond construction and maintenance since he was a young boy digging holes in his parents backyard and filling them with water. To those who know him Shawn is simply “the pond guy.”
