The exact methodologies involved vary, but they all involve walking along watercourses (usually in wet weather), looking for sediment or other pollution entering the watercourse and tracing it back to its source in the landscape.

Once sources of pollution have been identified, interventions can be delivered to mitigate them or disconnect the pollution pathway carrying pollutants to the watercourse. It is important to note that these surveys give a very quick snap-shot of the situation in a catchment (which by their nature are highly transient) and solutions must be enacted immediately to ensure success.

Perhaps the most extensive surveys of this kind have been undertaken by APEM on behalf of the Environment Agency. The APEM methodology has now been used by them and others to assess over 14,000km of river in the UK and they now offer training in the application of this method. APEM have recently developed the approach to identify diffuse urban pollution and have worked in partnership with Mersey Rivers Trust to trial the approach.