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Blackwater

Blackwater | Essex Rivers Hub

The Blackwater Operational Catchment

This operational catchment consists of 5 water bodies. The River Pant rises near Sewards End to the east of Saffron Walden. It is a predominantly rural catchment and flows in a south easterly direction through Great Sampford and Finchingfield towards Braintree, where it becomes known as the River Blackwater. The Balckwater name derives from a discharge from a textile works at Bocking which once turned the river black. From Braintree the river meanders its way through Coggeshall, Kelvedon and Witham, where it meets the River Brain, and on to Maldon before it empties into the Blackwater Estuary at Heybridge Basin.

The Blackwater Estuary is the largest estuary in Essex and one of the largest estuarine complexes in East Anglia, flowing from Maldon before joining the Colne Estuary and the North Sea at Mersea Island. The Blackwater and Colne estuaries are of international conservation importance and consist of a mosaic of important habitats including saltmarsh, intertidal mudflats, shingle, and coastal grazing marsh. These habitats support nationally scarce plants and rare invertebrates. Internationally and nationally important numbers of waterbirds also winter at the site.

The Blackwater Estuary is a 5,538-hectare biological Site of Special Scientific Interest (SSSI), with an area of 4,395 hectares also designated as a Ramsar Wetland of International Importance, and 1,099 hectares is a National Nature Reserve designated as a Special Protection Area (SPA). The River Blackwater supports a high class fishery and is an important source of public drinking water.

Blackwater Gallery

Pressures

The pressures for this waterbody are divided into categories: Diffuse Pollution, Fish Passage, Flow, Invasive Species, Physical Modification, and Point Source . Please click here to view these pressure descriptions in more detail.

Diffuse Pollution

This water body has developed problems with phosphate levels which contribute to its overall rating as poor. Unfortunately there is no data to suggest where these problems are originating from. The amount of phosphate fluctuates across the water body, but is likely to be causing this water body to fail for its macrophyte level too.

Flow

Flow has been investigated in this waterbody, but its effect on the ecological status is yet to be determined.

Invasive Species

Floating Pennywort has been most recently recorded on this water body in 2011 and 2012. Floating Pennywort covers the surface of the river, blocking out natural light and causing the plants below to die. The dead plants then rot down, removing the oxygen from the river. Floating Pennywort also causes trouble for boats, making the river very difficult to navigate.

Water Fern has been most recently recorded on this water body in 2012. This plant covers the surface of the river, blocking out natural light and causing the plants below to die. The dead plants then rot down, removing the oxygen from the river.

Japanese Knotweed has been most recently recorded on this water body in 2013. This plant not only shades out native plants, but also causes serious damage to buildings.

Signal Crayfish have been most recently recorded on this water body in 2002 and 2008. Signal Crayfish cause changes to the natural bankside habitat and also out-compete our native crayfish.

Turkish Crayfish have been most recently recorded on this water body in 2002. Turkish Crayfish cause changes to the natural bankside habitat and also out-compete our native crayfish. They are fierce predators and can completely change fish and invertebrate communities so that they are no longer in their natural state.

Chinese Mitten Crab have been most recently recorded on this water body in 2013. Mitten Crabs cause changes to the natural habitat as they modify the river banks, this can make them unsuitable for our natural species.

Giant Hogweed has been most recently recorded on this water body in 2013. This plant has been in the news a lot more recently due to the horrific burns that its sap can give the skin. This invasive plant is so large that it is able to shade out other native plants.

American Mink have been most recently recorded on this water body in 2009 and 2011. American Mink cause a wide range of problems on a river, including playing a large part in the local extinction of many natural species such as Water Voles and Kingfishers.

Himalayan Balsam has been most recently recorded on this water body in 2013. This pretty plant, with pink flowers, is fast growing and hardy. It covers river banks and shades out native plants. In the winter, Himalayan Balsam will die down, leaving bare banks that are susceptible to erosion.

The non-native invasive Signal Crayfish as well as the native White-clawed Crayfish are found in this water body.

Physical Modification

Multiple mitigation measures were put in place in order to improve the morphology of this water body which is currently classified as ‘moderate’. These mitigation measures were not taken forward.

Point Source

This water body has developed problems with phosphate levels which contribute to its overall rating as poor. Unfortunately there is no data to suggest where these problems are originating from. The amount of phosphate fluctuates across the water body, but is likely to be causing this water body to fail for its macrophyte level too. The River Blackwater failed tests for ‘Annex 10’ chemicals as traces of aromatic hydrocarbons were detected. These hydrocarbons are usually found in petrol, other fuel sources or when burning. Sewage treatment works have been identified as possible sources for these chemicals too.

Diffuse Pollution

This water body has developed problems with phosphate levels which contribute to its overall rating as moderate. Unfortunately there is no data to suggest where these problems are originating from.

Invasive Species

American Mink have been most recently recorded on this water body in 2009. American Mink cause a wide range of problems on a river, including playing a large part in the local extinction of many natural species such as water voles and kingfishers.

Point Source

This water body has developed problems with phosphate levels which contribute to its overall rating as moderate. Unfortunately there is no data to suggest where these problems are originating from.

Diffuse Pollution

Phosphate is classified as poor in this water body. The most likely diffuse pollution causes are agricultural and rural land management (poaching/runoff from arable land). There is also a possibility that the Ely Ouse transfer scheme is having an impact.

Flow

Flow is classified as ‘not high’ indicating that there are some issues with flow in this water body. This is also impacting dissolved oxygen levels.

Invasive Species

Signal Crayfish have been most recently recorded on this water body in 2004, 2007, 2008 and 2012. Signal Crayfish cause changes to the natural bankside habitat and also out-compete our native crayfish. They are fierce predators and can completely change fish and invertebrate communities so that they are no longer in their natural state.

Himalayan Balsam has been most recently recorded on this water body in 2013 and it covers an extensive area. This pretty plant, with pink flowers, is fast growing and hardy. It covers river banks and shades out native plants. In the winter, Himalayan Balsam will die down, leaving bare banks that are susceptible to erosion.

American Mink have been most recently recorded on this water body in 2009 and 2011 . American Mink cause a wide range of problems on a river, including playing a large part in the local extinction of many natural species such as water voles and kingfishers.

Giant Hogweed has been most recently recorded on this water body in the 1990s and 2012. This plant has been in the news a lot more recently due to the horrific burns that its sap can give the skin. This invasive plant is so large that it is able to shade out other native plants.

Physical Modification

This water body is classified as heavily modified for flood protection and as part of the Ely Ouse water transfer scheme.

Point Source

Phosphate is classified as poor in this water body. The probable cause is sewage outlets. Dissolved oxygen is classified as poor in the water body, one factor impacting this is sewage outlets, especially when flow is low and temperatures are high.

Diffuse Pollution

This water body has developed problems with phosphate levels which contribute to its overall rating as poor. Unfortunately there is no data to suggest where these problems are originating from.

Invasive Species

Himalayan Balsam has been most recently recorded on this water body in 2013. This pretty plant, with pink flowers, is fast growing and hardy. It covers river banks and shades out native plants. In the winter, Himalayan Balsam will die down, leaving bare banks that are susceptible to erosion.

Japanese Knotweed has been most recently recorded on this water body in 2007 and 2012. This plant not only shades out native plants, but also causes serious damage to buildings.

Floating Pennywort has been most recently recorded on this water body in 2012. Floating Pennywort covers the surface of the river, blocking out natural light and causing the plants below to die. The dead plants then rot down, removing the oxygen from the river. Floating Pennywort also causes trouble for boats, making the river very difficult to navigate.

Point Source

This water body has developed problems with phosphate levels which contribute to its overall rating as poor. Unfortunately there is no data to suggest where these problems are originating from.

Catchments

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Pressures

The topics below represent the pressures that many waterbodies in the Combined Essex catchment face. They have been divided into six main categories, but it is quite often that these categories can overlap as pressures relate to each other.

Diffuse pollution occurs as water moves across the land or through the ground and picks pollutants. These pollutants can come from a variety of places, including urban and field run off. The pollutants that enter the river can range from sediment to toxins to excess nutrients, meaning that diffuse pollution can cause a whole range of different issues. The variety in these pressure groups means that it is something that can be quite difficult to tackle. It requires groups of people, business and stakeholders to work together in order to solve this problem.

Fish should be able to travel up and down a river freely, allowing them to move and breed in the most suitable habitats for them. It is important that fish populations do not become isolated, as this makes them more susceptible to disease and puts pressure on their survival. Unfortunately, there are often many barriers along rivers that prevent fish from being able to migrate up and down stream. Where barriers have been identified, they will be seen as a ‘pressure’ on a waterbody. Thankfully, there are many solutions now that can be put in place to aid fish passage, even over large barriers.

The flow in a river can vary greatly throughout the year as rainfall and run off can have an effect. This is a natural process. It is when flow is impacted by non-natural processes that it can cause problems. Sometimes, water can be intercepted or removed from a system; this will reduce the flow, therefore changing the habitat conditions. Some species are happy in high energy rivers. This means that when flow is reduced, these species will no longer survive. The opposite of this can occur when excess water is entering a river, for example through increased runoff. Low energy systems then become high energy and displace the species that live there.

A species that is not meant to be found in a particular area is known as an invasive species. Invasive species can be from a different habitat or a different country altogether. Most of the invasive species that we find on our rivers have come from other countries – plants that people have imported for their gardens or animals that have been released for food or by animal rights activists. Control of invasive species requires a lot of time and effort. We are fortunate that we do have a range of methods to manage most of the invasive species that cause havoc on our rivers, but there are still some which we are still struggling to control.

Many of our rivers have been heavily modified over the years as rivers have been used for a wide range of purposes. Physical modification is one of the biggest factors that causes our rivers to be unhealthy. The issues that it can cause range from reducing habitat, preventing migration of mobile species, and even have an effect on the water quality. Where structures and modifications are no longer in use or necessary, they should be removed to allow the river to regain its natural state. Unfortunately, this action is not always taken which means that many of our rivers are over straightened and contain redundant structures. It is possible to return a lot of our rivers to their natural state, through one off projects, but in other cases it is not possible as the river has been changed to protect assets or manage flooding. It is recognised that some modifications cannot be removed without having severe negative impacts both socially and economically.

This is pollution that comes from a single identifiable source. The pollution entering the river could include a whole range of pollutants. Some point source pollution is known about and licences, for example sewage treatment works. Other sources are not licensed, and therefore work needs to be done with landowners to fix the problems that are allowing the pollution to enter the river. Point source pollution is more easily controlled than diffuse pollution as it often only takes one management approach to solve the issue.