• People and the River

Pathogens in Rivers: what are they and how do they impact rivers?

Rivers have become a regular feature in news headlines about the environment as they face a wide range of pressures from human activity. While wastewater often dominates these headlines, it represents only one part of a much bigger picture. Our rivers can be affected by many different pollutants and factors, each with its own sources, behaviours and potential impacts on wildlife and people. Understanding what these pollutants and other factors are, how they enter our waterways, and what levels are considered safe is an important step in protecting and restoring healthy river ecosystems.

 

What are they?

Pathogens are defined as microorganisms, such as bacteria, viruses and protozoa, that can spread diseases. In river environments, common groups of these pathogens include:

  • Bacteria such as E. coli, Salmonella and Campylobacter
  • Viruses such as norovirus, adenovirus and hepatitis A
  • Protozoa such as Cryptosporidium and Giardia

 

These pathogens typically originate from the faecal waste of humans, livestock and wildlife – while most occur naturally at low levels, it is often human activity that can increase their concentrations in rivers, raising ecological health and public safety risks.

They can enter our local waterways through numerous ways, including:

  • storm overflows – heavy rainfall can overwhelm sewer systems, releasing diluted sewage directly into rivers
  • agricultural runoff – manure, slurry and livestock waste often washes into our watercourses during rainfall
  • urban runoff – contaminated surface water can enter our drainage systems
  • septic tanks – poorly maintained or leaking systems can discharge pathogens into groundwater and nearby water bodies
  • wildlife – local fauna contribute naturally, although at much lower levels than human and agricultural sources

 

Since pathogens are a biological pollutant rather than chemical, their presence can fluctuate rapidly in rivers depending on the level of rainfall, temperature, flow conditions and land use.

 

 

Pathogens in Rivers: what are they and how do they impact rivers? | Essex Rivers Hub

A bridge in Ufford that crosses the Deben, which flows on to Woodbridge and Felixstowe Ferry by Guy Campbell

 

What are the impacts?

Pathogens pose a significant challenge as they affect rivers, their associated wildlife and human health in multiple interconnected ways. In water, pathogen levels can fluctuate rapidly with the environmental conditions and they can survive for long periods in sediments, wet soils and biofilms. Sediments in particular can act as stores for pathogens, releasing them back into the watercourse during high flows or disturbance. As they are also difficult to monitor consistently, frequent sampling is often required and even low concentrations can pose direct risks to human health.

For example, pathogens in rivers can cause illness through:

  • recreational contact – swimming, paddling, angling, watersports etc.
  • drinking water abstraction – where rivers/groundwater feed public supplies
  • food contamination – particularly shellfish harvested from estuaries that are exposed to upstream pollution

Some illnesses that are linked to pathogen exposure can range from gastrointestinal infections to more serious conditions in vulnerable individuals.

 

In addition, some pathogens can also have a significant impact wildlife, including:

  • stress or disease outbreaks – this may affect fish and amphibian populations in heavily contaminated waters
  • habitat degradation – high pathogen loads often coincide with low oxygen and poor water quality, negatively affecting invertebrates and aquatic plants
  • accumulation – shellfish in estuaries can accumulate pathogens, affecting both wildlife health and food safety

In summation, pathogen pollution rarely occurs in isolation and is often accompanied by elevated nutrient levels, excess ammonia and organic matter and reduced levels of dissolved oxygen. These combined pressures can alter river ecology, reduce biodiversity and disrupt natural processes.

 

As pathogens come from multiple sources, no single intervention is sufficient; a common theme among the river pollutants we have explored thus far in this series of articles. Key things to prioritise in addressing for this particular pollutant are:

  • reducing inputs at the source – such as improving sewer infrastructure and ensuring septic tanks are properly maintained
  • improving treatment and management – perhaps by installing wetlands to naturally filter pathogens before they reach the river
  • strengthening monitoring and public information – through clearer public reporting of sewage spills and pollution events and involvement of citizen science in tracking local water quality trends

 

Overall, pathogens as river pollutants are a widespread and growing concern, but through improved monitoring, stronger regulation and partnership working, pathogen inputs can be reduced and our river ecosystems can be better protected. By increasing our understanding of how pathogens behave, where they originate from and their impact on rivers, we can work together to design more effective and long-term solutions that help safeguard the health of communities and wildlife in the future.

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Pressures

The topics below represent the pressures that many waterbodies in the Combined Essex catchment face. They have been divided into six main categories, but it is quite often that these categories can overlap as pressures relate to each other.

Diffuse Pollution

Diffuse pollution occurs as water moves across the land or through the ground and picks pollutants. These pollutants can come from a variety of places, including urban and field run off. The pollutants that enter the river can range from sediment to toxins to excess nutrients, meaning that diffuse pollution can cause a whole range of different issues. The variety in these pressure groups means that it is something that can be quite difficult to tackle. It requires groups of people, business and stakeholders to work together in order to solve this problem.

Fish Passage

Fish should be able to travel up and down a river freely, allowing them to move and breed in the most suitable habitats for them. It is important that fish populations do not become isolated, as this makes them more susceptible to disease and puts pressure on their survival. Unfortunately, there are often many barriers along rivers that prevent fish from being able to migrate up and down stream. Where barriers have been identified, they will be seen as a ‘pressure’ on a waterbody. Thankfully, there are many solutions now that can be put in place to aid fish passage, even over large barriers.

Flow

The flow in a river can vary greatly throughout the year as rainfall and run off can have an effect. This is a natural process. It is when flow is impacted by non-natural processes that it can cause problems. Sometimes, water can be intercepted or removed from a system; this will reduce the flow, therefore changing the habitat conditions. Some species are happy in high energy rivers. This means that when flow is reduced, these species will no longer survive. The opposite of this can occur when excess water is entering a river, for example through increased runoff. Low energy systems then become high energy and displace the species that live there.

Invasive Species

A species that is not meant to be found in a particular area is known as an invasive species. Invasive species can be from a different habitat or a different country altogether. Most of the invasive species that we find on our rivers have come from other countries – plants that people have imported for their gardens or animals that have been released for food or by animal rights activists. Control of invasive species requires a lot of time and effort. We are fortunate that we do have a range of methods to manage most of the invasive species that cause havoc on our rivers, but there are still some which we are still struggling to control.

Physical Modification

Many of our rivers have been heavily modified over the years as rivers have been used for a wide range of purposes. Physical modification is one of the biggest factors that causes our rivers to be unhealthy. The issues that it can cause range from reducing habitat, preventing migration of mobile species, and even have an effect on the water quality. Where structures and modifications are no longer in use or necessary, they should be removed to allow the river to regain its natural state. Unfortunately, this action is not always taken which means that many of our rivers are over straightened and contain redundant structures. It is possible to return a lot of our rivers to their natural state, through one off projects, but in other cases it is not possible as the river has been changed to protect assets or manage flooding. It is recognised that some modifications cannot be removed without having severe negative impacts both socially and economically.

Point Source

This is pollution that comes from a single identifiable source. The pollution entering the river could include a whole range of pollutants. Some point source pollution is known about and licences, for example sewage treatment works. Other sources are not licensed, and therefore work needs to be done with landowners to fix the problems that are allowing the pollution to enter the river. Point source pollution is more easily controlled than diffuse pollution as it often only takes one management approach to solve the issue.