Constructed wetlands are engineered systems that use water, plants, growing media and naturally occurring microorganisms to improve water quality. Fungi are one part of this biological community. They may help break down some organic pollutants, support microbial activity and contribute to the filtering or retention of contaminants in suitable wetland designs.
For councils and municipal remediation teams, the most useful question is not whether fungi can replace a constructed wetland. They cannot. The practical question is whether fungal activity could improve a particular treatment stage, help manage a difficult pollutant or provide a low-impact option alongside established engineering controls.
What role can fungi play?
Fungi produce networks of fine filaments, known as hyphae, and release enzymes that help them digest complex organic material. In soil, compost and wetland media, fungal hyphae can also provide surfaces where other microorganisms grow. This means fungi may influence treatment directly and indirectly.
In a constructed wetland, fungi may:
- help transform or break down some organic compounds, particularly where the compounds are difficult for other microorganisms to use;
- contribute to the decomposition of plant litter and other natural carbon sources;
- support a diverse microbial community on plant roots and within wetland media;
- help bind or retain some contaminants in fungal biomass or surrounding material; and
- contribute to the physical structure of media, although this effect is unlikely to be sufficient on its own for reliable hydraulic treatment.
These processes depend on the fungal species, pollutant, water chemistry, temperature, oxygen conditions, media, residence time and overall wetland design. Fungi are not universal pollutant removers. A result observed in a laboratory container may not translate into dependable treatment at a council site.
How fungi interact with plants and microorganisms
Constructed wetlands work through several connected processes. Plants slow water movement, take up some nutrients and provide root surfaces. Bacteria and other microorganisms transform many dissolved pollutants. The growing media can filter particles and provide places for chemical and biological reactions. Fungi operate within this wider system rather than separately from it.
Fungal hyphae can grow through media and around plant roots, where they may interact with root-associated microorganisms. Fungi and plants may sometimes exchange nutrients or influence each other’s access to water and dissolved compounds. In other situations, fungal growth may compete with plants or other microorganisms for space and resources. These relationships are site-specific and should not be assumed to occur simply because fungi are added.
Plant health remains important. Healthy vegetation can support a stable wetland, but plant roots do not guarantee that a particular pollutant will be removed. Similarly, visible fungal growth is not evidence that treatment is working. Water-quality monitoring is needed to establish whether the complete system is performing its intended function.
Where fungal approaches may be worth investigating
Fungal applications may be considered where a constructed wetland is already appropriate and there is a specific treatment challenge that conventional stages do not fully address. Possible areas for investigation include water containing biodegradable or partly biodegradable organic pollutants, stormwater or runoff with complex organic residues, and polishing stages where a lower-intensity biological process may be suitable.
Fungi may also be relevant when a council is assessing a media amendment or a contained biological treatment unit before water enters a planted wetland. In these situations, the fungal component can be isolated, monitored and removed or replaced if it does not perform as expected.
Use should be more cautious where the main concern is a highly toxic, persistent or mobile contaminant, or where treatment failure could quickly affect a sensitive receiving environment. Fungal processes may transform a compound without fully destroying it, or may move contamination into biomass or solids that then require controlled management. They should therefore be assessed as one treatment step, not assumed to provide complete remediation.
Ways fungi could be incorporated
Allowing naturally occurring fungi to contribute
The simplest approach is to design and operate the wetland so that naturally occurring fungi can function within the media and root zone. Suitable moisture conditions, organic matter, aeration patterns and plant establishment may support a diverse microbial community without deliberate inoculation.
This approach is generally easier to manage and may have fewer biosecurity and permitting concerns. It also provides less control over which fungi are present and how strongly they contribute to treatment. The system must still be designed around proven wetland principles, hydraulic control and the target pollutants.
Using fungal-active media or contained materials
A separate bed, cartridge, biofilter or media layer could potentially provide a controlled environment for fungal activity. Any material used would need to be compatible with the water chemistry, hydraulics and maintenance plan. It should not introduce harmful substances, create excessive oxygen demand, release fine particles or wash out into the receiving environment.
Using a contained treatment stage can make inspection and replacement more practical than attempting to distribute fungal material throughout a large wetland. It may also allow a council to compare fungal media with an existing media type under similar operating conditions.
Deliberate inoculation
Adding selected fungal cultures is a more specialised and less established option. The organism would need to be identified, assessed for safety and environmental compatibility, and shown to remain useful under actual site conditions. Deliberate release should not be undertaken casually, particularly where non-local organisms, modified organisms or material of uncertain origin could be involved.
Any inoculation proposal should be reviewed with relevant environmental, biosecurity and public health authorities. It should also include controls for storage, transport, worker exposure, containment and end-of-life disposal. A council should never release unverified fungal material into a wetland simply because it has shown activity in a small-scale test.
Design and operational considerations
Before adding a fungal component, establish the treatment objective and the limitations of the existing system. Important questions include:
- Which pollutants are present, and are they dissolved, particulate or attached to sediment?
- What are the likely inflows, flow variations, temperature range, pH and oxygen conditions?
- Will the wetland receive untreated peaks that could damage plants or biological communities?
- Where will solids, dead plant material and spent media go?
- Can the proposed fungal stage be isolated, bypassed, inspected and maintained?
- What conventional treatment or wetland improvement should be compared with the fungal option?
Hydraulic design is especially important. Short-circuiting, clogging or excessive flow can reduce contact time and undermine any biological process. Pre-treatment may be needed to remove coarse solids, oils or other materials that could block media or harm the biological community. Fungi should not be used to compensate for inadequate sediment control, poor drainage, unsuitable loading or missing safety controls.
Monitoring and evidence
Monitoring should cover both treatment performance and system condition. Depending on the site, this may include flow, turbidity, suspended solids, nutrients, relevant organic pollutants, pH, oxygen conditions and indicators of plant and media health. Samples should be collected at appropriate points before and after the proposed fungal stage, with enough repeated observations to account for changing conditions.
Monitoring fungal presence alone is not enough. The key question is whether the whole system produces a reliable improvement without creating new risks. A pilot should define success and failure criteria in advance, include a comparison with an established treatment approach and record maintenance demands. If transformation products or contaminated biomass could be produced, these should be considered in the sampling and waste-management plan.
Safety, permitting and environmental responsibility
Fungal materials can contain spores, allergens or other biological hazards. Workers may need suitable procedures and protective equipment for handling cultures, colonised media, sludge and plant residues. Odour, aerosol generation and contact with contaminated water should also be considered in site planning.
Permits or approvals may apply to changes in water treatment infrastructure, discharge quality, waste handling, biological material use, vegetation removal or release of organisms. Requirements vary by location and project type, so early discussion with the relevant authorities is advisable. Materials should be traceable, appropriately contained and managed at the end of their useful life.
A realistic pathway for councils
Fungal treatment is most credible when it is treated as a targeted enhancement to a well-designed constructed wetland. A sensible pathway is to begin with a site assessment, review existing performance, identify a specific treatment gap and compare fungal and non-fungal options. Small-scale testing can then determine whether the proposed approach works with the actual water, media and operating conditions.
If results are promising, a contained pilot with clear monitoring, maintenance and stop criteria can provide stronger evidence before any larger installation. The final decision should consider capital and operating costs, staff capability, replacement materials, waste management, regulatory obligations and long-term reliability—not only pollutant removal in a controlled test.
Fungi may offer useful biological functions in some constructed wetlands, especially as part of a broader treatment train. Their value will depend on careful design, local assessment and evidence from the site in question. For most councils, the best starting point is not widespread fungal release, but a controlled investigation of whether fungal activity can safely and affordably improve an existing or planned wetland system.