The Crane Valley Partnership

Water Quality

Due to the urbanised nature of the Crane catchment, it is typically subject to pollution, both direct and diffuse. Pollution has been present on the Crane for several hundred years, although changing in type, source and intensity.

Surface Water Runoff

Surface water runoff has an impact on the water quality of the river. This is due to surface water picking up contaminants as it drains from the urban landscape and flows into the river. Contaminants that create the greatest impact to surface waters include petroleum substances, herbicides and fertilisers. High levels of these chemicals can cause serious damage to aquatic life, affecting fish at every life stage, and cause illness in birds. Surface water runoff can cause major problems in the river during periods of high temperature, when oxygen levels are naturally lower and fish are more vulnerable.

The Crane also suffers from high levels of glycol when freezing temperatures coincide with heavy rainfall. In freezing conditions glycol is used by Heathrow Airport as an anti-freeze agent. Heavy rainfall may then overload the treatment capacity of the airport’s reservoirs and excess glycol may be discharged into the Crane. Its effects can be seen in the river as grey fungus and although it is unproven to have a direct effect on aquatic life, glycol does raise the biological oxygen demand (BOD) of the river. Increased BOD leads to lowered levels of dissolved oxygen (DO) and this can be detrimental to aquatic life forms that cannot tolerate low levels of DO. As part of their management strategy, Heathrow Airport has a monitoring programme to manage the land they own.

Sewage Misconnections

It is easy to assume that river pollution comes from places like factories, farms and industry. Yet, in many cases the pollution in our rivers comes from a much less obvious source - our homes. Incorrect plumbing could mean that waste water from dishwashers, washing machines, sinks, baths and even toilets is flushed directly into a local river. People doing their own plumbing and even professional plumbers can accidentally create these misconnections. These 'misconnected' pipes are a common cause of pollution to rivers and streams, especially in towns and cities.

When untreated sewage enters our rivers, DO can drop significantly and ammonia levels may become toxic to fish. Grey fungus is typically seen on the bed and banks of the watercourse, or on other structures such as outfall pipes and gullies.

The Environment Agency and Thames Water are identifying polluted outfalls and surveying the entire catchment to identify misconnected properties. Once the misconnection has been demonstrated to the property owner they must arrange for the problem to be resolved.

Further Information

Helping to correct misconnections - Connect Right
Reducing the risk of blocked sewers - Guidance on fat, oil and grease disposal
Report pollution incidents - 0800 80 70 60