The murky world of sediment pollution and its impacts on fish.

Naturally Compliants Peter Matthews delves in to the impacts of sediment laden water from construction sites finding its way in to fish supporting water courses. He also provides advice on how to get the message across.

For an Environmental Clerk of Works (ECoW) working on a construction site, one of the greatest challenges is preventing the escape of silty water into the aquatic environment such as streams, rivers and lakes. The status of dirty water as a pollutant and the ecological damage it can cause is not always fully understood on construction sites.

A common misconception is that because silt and silty water is non-toxic, non-corrosive and non-flammable it will do little harm to the ecology of a water body. This is not the case, however, and examples of the harm it can cause include the following:

  • Causing suffocation of fish by blocking gills,
  • Blinding of gravel beds causing disruption to spawning fish or failure to spawn,
  • Visual impairment of fish causing a reduction in predation success,
  • Smothering of aquatic invertebrates and loss of habitat, and
  • Reduction in dissolved oxygen if the silt contains significant organic material (the biological oxygen demand).

Legally, pollution, in relation to the water environment, means the direct or indirect introduction, as a result of human activity, of substances (including bacteria and other pathogens) or heat into the water environment, or any part of it, which may give rise to any harm. Therefore, in addition to the physical impacts, sediment entering the water environment as a result of construction activities would therefore meet the definition of pollution and should be treated as such.

A conscientious site operative who has been trained in emergency response is likely to react quickly and appropriately to a serious pollution incident such as an oil spill. But that same operative may not respond in the same way to a silt pollution incident, through a lack of knowledge of its potential to cause damage.

Courses and tool box talks (TBTs) can be used to raise awareness of silty water but these need to be made engaging. Making the connection between silty water and the negative effect it has on fish populations, and therefore fishing, is one way of presenting the problem in the context of a widely practiced hobby. Whatever approach is taken, more needs to be done to communicate the message that silt pollution is a serious environmental issue on a construction site.