pond ecology

Ecology by definition is the relationship between organisms and their environment. The term “natural balance” often arises in discussion regarding pond keeping. Unfortunately, many people defer to this believing it will serve them well in their overstocked and poorly filtered ponds

The fact is the typical backyard pond is not natural - it is manmade and requires advanced filtration technology. A natural stone bottomed pond will generally not sustain over time as touted by some pond builders
This toad found a warm spot for Winter

Natural Pond vs. Koi Pond

A pond as defined is a body of water that allows macrophytic growth throughout its basin. Basically that means that plants can grow on the whole bottom - the depth is likely no greater than 15 feet.

Another definition deals with turnover - a pond is shallow enough to turnover by the wind alone, not requiring drastic air temperature changes.Turnover is simply mixing of water from top to bottom

This mixing can be dangerous during the Winter, as explained here. Deeper dimictic lakes turn over only in the Spring and Fall, while our backyard pond will turn over much more frequently.

A koi pond is not simply a pond with koi in it. Sure you need koi, but you also need bottom drains and advanced filtration to deal with the huge bio load of fish that does not exist in a natural pond

high fish loads

Our ponds are small closed systems with Eutrophicwater rich in organics and minerals which promote algae growth thereby reducing the available oxygen in the water loads while we expect OligotrophicThese lakes have high Oxygen contents and visibility due to the lack of nutrients. Fish, phytoplankton, plants, zooplankton etc. are present in small populations visibility and characteristics. Our ponds may have 10 fish in 1,000 gallons, while a natural body of water only 1 fish in 10,000 gallons. In the case of watergardens, hobbyists often expect everything to survive in harmony when introduced in just a weekend or two. The bio diversification is limited in our backyards due to the habitat and the high fish load

Koi pond parameters do not compare to a natural pond or lake that is many times larger and has evolved over a long period of time developing a mature food web. A natural balance in lightly stocked unfiltered ponds can arrive once bacteria and plants have sufficiently rebounded from Winter, but this is not until the early Summer. Water quality is paramount and must be viewed as a 24 hr. 365 day proposition, so a purely natural approach will not suffice in an unatural setting

Bacteria, Phytoplankton, Zooplankton, Macrophytes and of course Koi are the main ecological players [Trophic Levels] that a pond keeper should have a good grasp of. The lower trophic levels require a far greater populous in order to overcome the poor ecological efficiency found in nature. A trophic level is simply a group of organisms that occupy the same location in the food chain

The Microbial Loop

Only fully grasped in the last 30 years, the microbial loop consists of tiny microscopic organisms including bacteria, ciliates and flagellates. These nano and pico sized plankton break down the POM [particulate organic matter] that we find accumulating on the bottoms of our ponds. In ponds with ineffectual filters and/or no bottom drains, the detritus builds up creating more BOD [biological oxygen demand]. Simply put a dirty pond requires more oxygen than a clean one - anoxic conditions could be created which can stress and kill our fish

Particulate can also accumulate to such levels that it goes anaerobic [without oxygen]. At this point pathogenic bacteria begin to proliferate potentially causing a disease state in our fish. This swings the balance of bacteria of which most are neutral to one where pathogenic predominate. Detritus can also be in suspension in the the water column causing turbidity [unclear water]. Ideally it is best to remove this debris with a bottom drain which operates like a vacuum, removing particulate to a settlement chamber. This is necessary to maintain the natural balance in a fish pond


Algae, primary producers, are ubiquitous and land as spores in our ponds. Both string and planktonic algae are natural and impossible to prevent - they are not the sign of an unhealthy pond. A planktonic [free floating] algae bloom will turn the entire pond green very quickly and often subside in the same manner once the resources, namely phosphorus and nitrogen, have been exhausted. UV Clarifiers are used to control green water, and they work very well at this.

String algae
can take many forms. Typically green, filamentous type grows on the liner, stone and waterfalls. A short carpet is desired, but long strands are a cosmetic nuisance and can be removed physically or controlled with commercial products like "Pond Balance" and barley straw


These are small to microscopic animals comprised of 3 main categories - Protozoa, Rotifers and Crustaceans/insect larvae. The term plankton [same applies with phytoplankton] means "a lack of OR very little controllable motility". In other words, they free float around in the water column at one with the currents

Some examples of Zooplankton that are of real consequence to the pond keeper are potentially lethal protozoa parasites such as obligateA parasitic organism that requires a host in order to complete its life cycle Costia and Tichodina. Other Zooplankton like Daphnia are beneficial and utilized to feed planktivours like our koi fry and small goldfish. Rotifers are commonplace, mostly microscopic and the Monogonata class [90%] predominates fresh water littoral zones.The shallow sunny shoreline planted areas of a pond or lake Zooplankton fill a vital niche in the food chain feeding on bacteria + algae thereby breaking down matter. They themselves providing food for fry and small fish


Plants are primary producers [produce biomass from carbonless compounds] that play a large role as oxygenators through Photosynthesis. Remember, submersed waterplants consume oxygen at night, even the roots of emergent bog plants too - so a good aeration system needs to be in place and running 24/7. If you have a waterfall only, do not turn it off at night and increase aeration during hot and/or stormy weather

In a koi pond scenario, most plants are best sequestered from the koi [in a header pool for example]. In the case of a vegetable filter, one must realize that they take some time to get established so you must rely on other forms of bio filtration, particularly in the Spring. Besides soaking up Nitrates, vegetable filters are also great at supporting colonies of bacteria for nitrification, filter feeders [ie rotifers] to remove algae and root systems to trap larger solids

Why Ponds with Rock Bottoms Do Not Function

Man made ponds are not natural due to the inevitable huge bio load [fish load] that exist in our ponds. In a natural body of water, the ratio of bacteria, phytoplankton, zooplankton and macrophytes [trophic levels] is huge in comparison to the comparatively low fish population - therefore they can flourish without habitat destruction and over predation. This framework is required to maintain clear water and a healthy balanced environment

In our backyard ponds, these other trophic levels are out of balance as fish consume zooplankton and plants. Because of the over abundance of fish, your pond will not function anything like a natural system which has evolved over a long period of time. This is why a proper filter system is required to maintain the water clarity and quality in your fish pond

The subjective individuals who promote 2 foot deep rock bottomed ponds either lack education or care more about their money making agenda. Remember, full pond cleanouts are expensive and are a lot of work. If a bottom drain is installed, the pond doesn't need to be drained and cleaned - EVER. I call it "Selective Science". If the science fits the agenda, then it is accepted. If not, it is refuted - quite poorly I might add as evidenced in the "myth busting" diatribes on some websites

Read more about why these systems are not ideal in our reviews section



This pond is a little easier to clean because their are no rocks - with a bottom drain it would be self cleaning