01/09/2026
Phosphates, nitrates and ammonia can all have significant impacts on salmon and trout and the quality of the habitats they depend upon, although they affect the river environment in different ways.
Excessive phosphate is primarily a nutrient pollution problem. Phosphate can stimulate excessive growth of algae and aquatic plants. When this vegetation dies and decomposes, the process consumes dissolved oxygen in the water. This can result in periods of low oxygen, particularly during warm weather and at night, creating stressful conditions for salmon and trout. Excessive algal and plant growth can also alter the structure of the river, reduce light pe*******on, change aquatic plant communities and affect the abundance and diversity of aquatic invertebrates that provide an important food source for fish.
Nutrient enrichment can also contribute to the accumulation of organic material and fine sediment within the riverbed, potentially reducing the quality of spawning and juvenile habitat.
Nitrate is generally less directly toxic to salmon and trout than ammonia, but elevated nitrate concentrations can contribute to nutrient enrichment and eutrophication. Increased nitrate availability can promote excessive plant and algal growth, which can subsequently cause fluctuations in dissolved oxygen as vegetation grows, respires and decomposes. Changes in vegetation and water quality can also alter aquatic invertebrate communities and reduce the quality of feeding habitat available to salmon and trout. Therefore, nitrate can have an important indirect effect on salmonid populations by contributing to the deterioration of the wider river ecosystem.Ammonia is different because it can have a direct toxic effect on fish. Ammonia occurs in water in different forms, with unionised ammonia, NH3, being considerably more toxic to fish than the ionised form, NH4+. Salmon and trout are particularly sensitive to elevated ammonia concentrations. Exposure to excessive ammonia can damage the gills, interfere with respiration and the regulation of salts within the fish, cause physiological stress and impair feeding, growth and swimming ability.
At sufficiently high concentrations, ammonia can result in fish mortality. The proportion of ammonia present in the more toxic unionised form increases as water temperature and pH increase, meaning that the same total ammonia concentration can present a greater risk under warmer and more alkline.. Ammonia can add an additional pressure because it can directly affect the health and survival of salmon and trout. Together, these pressures can reduce the quality of feeding, nursery and spawning habitat and ultimately affect the ability of a river to support healthy salmon and trout populations.
It is therefore important when assessing a salmonid river to consider phosphate, nitrate and ammonia alongside dissolved oxygen, pH, temperature, suspended sediment, fine sediment deposition and the condition of spawning gravels and where it is known to be a persistent issue.There are methods that can be used nature based and green engineering mixed with grey engineering methods and practices that can reduce these elements impacts our rivers.We are working on a project regarding this at the moment so we will bring this forward when we have completed the theory planning and move to seeking permissions in testing our hypothesis on reducing pollution.
In our group we are lucky to have members with river processing,water quality,fish habitat and wildlife training and qualification with river restoration planning as well as instream macroinvertebrate monitoring on four different instream survey methods.With the free time we give we will use these skills to work towards better habitat for fish applying science theory and testing hypothesis and understanding results to progress to a suitable piloy project plan of action in conjunction and approval of all agencies charged with environment protection so watch what we get upto in 2026.
