Aquatic Consultancy Service                            WQR0021


Written evidence submitted by Dr Bernice Brewster, Aquatic Consultancy Service



Monitoring Water Quality

I have been working in the freshwater environment for in excess of 30 years and during this time, I have been shocked by the increasing loss of diversity and numbers of aquatic macroinvertebrate life in our rivers and streams.  Aquatic macroinvertebrates have traditionally been used as a key tool for biotic assessment for the quality of freshwaters (e.g. RIVPACS, FBA Guide to British Freshwater Macroinvertebrates for Biotic Assessment, Dobson, M. et al. 2012 Guide to Freshwater Invertebrates).  Increasing budget cuts have reduced the capacity for the Environment Agency to make routine assessment of our rivers and streams, only conducting macroinvertebrate assessments following severe pollution incidents.  As a consequence over the years, I have witnessed a significant decline in both diversity and numbers of freshwater macroinvertebrates due to permitted and diffuse pollution.

The lack of routine macroinvertebrate assessment has allowed at least five species of non-native crayfish to become established on many rivers and streams in southern Britain.   These non-native crayfish are destructive leading to erosion of the banks of rivers and streams, causing sediment to pollute the water and loss of aquatic macroinvertebrates.  The River Chess in the Rickmansworth area is a classic example of the destruction caused to the banks and water course, having personally conducted a survey on behalf of TFL in this area, the river was devoid of native macroinvertebrates. 

The routine monitoring of rivers and streams for both the chemical water quality and diversity of aquatic macroinvertebrate life is essential if the quality of river and streams are to be improved.


a) Sewage pollution

The release of sewage into rivers during periods of heavy rain is an obvious and unacceptable pollution of many rivers, there is however a further source of sewage pollution of rivers and streams which is affecting many of our freshwater habitats.  In rural areas, without access to mains drainage systems, household effluent is treated in biological treatment plants.  Whilst these plants effectively reduce the solid waste, they produce an ammoniacal liquor, together with anthropomorphic produced chemicals plus both prescription and recreational drug residues which are released into adjacent rivers and streams.  Such disposal of effluent is regarded as acceptable under planning consents, without due consideration of the damage being done to all aquatic life.  It is assumed the disposal of the effluent will be rendered harmless due to a dilution effect but where chalk streams are quite small, but during the intense summer temperatures we have experienced in recent years low stream flows can allow these discharges to form a toxic flow.  An example is the Goddington Chalk Stream, flowing from the North Downs in Kent, which is being increasingly subject to discharge from biological effluent treatment.

Planning consents should be more rigorously enforced to reduce permissible effluent or enforce settlement lagoons using reed beds to clean the waste before discharge into streams and rivers.

b) Farm pollution

While there has been considerable effort to reduce nitrate entering streams and rivers, over the years I have encountered increasing concentrations of phosphate polluting freshwaters.  Increasingly digestate is being spread onto fields to increase crop production but in many instances these are over used. Phosphate coupled with nitrate are leading to increasing Cyanobacterial blooms (blue-green algae) on many lakes which feed the rivers and streams.  Cyanobacteria are extremely toxic to mammals, they are an extreme nuisance on the affected lakes but receive little attention as the lakes are presumed to act as a treatment plant, the blue-green algae reducing the excessive nutrient load before the water enters the stream and rivers.  These blooms on lakes should act as an indication that excess nutrients are finding their way into our freshwaters.

Measures to monitor use of farm fertilizers would be advisable to reduce nutrient levels ultimately entering streams and rivers.

Since WW2, we have changed farming practices significantly, giving rise to larger fields with shallow rooted crops and although there is supposed to be a 5m buffer zone for wildlife around each field this is not well practiced.  During periods of heavy rain, eroded soil readily washes off the fields (Figure 1), into the streams and rivers giving rise to high suspended solids, which damages delicate gill tissues of both fish and aquatic invertebrates.  The turbidity cuts out light in the rivers and streams affecting the submerged aquatic vegetation, which is important habitat for all aquatic animals.

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Figure 1. Soil erosion from adjacent fields


Perhaps enforcing the use of wildlife buffer zones for all farms would be a helpful mechanism for reducing soil erosion followed by over use of fertilizers to compensate for loss of nutrients resulting from the loss of topsoil.


In the UK we have a very cavalier attitude to our streams and rivers and pollute and damage them without a second thought.  There are just 200 chalk streams in the world of which 85% are found in the UK, we have a duty to preserve these unique habitats and their fauna and flora.


February 2021