2024 Bathing Water Profile for Mawgan Porth
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Mawgan Porth is on the north coast of Cornwall. It is a rural, sandy beach, approximately 720 metres wide, backed by sand dunes and cliffs. The River Menalhyl flows across the beach to the sea.
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Cornwall
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Cornwall
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The Environment Agency have periodically carried out additional catchment monitoring alongside routine bathing water monitoring. We have used a DNA tracing technique to help us identify whether sources of faecal pollution are animal or human. This can help us target further investigations to pinpoint pollution problems and improve bathing water.
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There is an emergency/storm overflow from the Trenance Porth pumping station, that discharges to a tiny stream 230m north of the Environment Agency monitoring point. There is also an emergency/storm overflow from the Mawgan Porth pumping station, that discharges to the River Menalhyl 150m from the beach. The operation of the overflows can lead to a temporary drop in water quality in the receiving waters and at the bathing water. This bathing water is included in the Surfers Against Sewage “Safer Seas Service”. This service can alert you to Combined Storm Sewer Overflow discharges via a phone App and in addition, it includes the Environment Agency Pollution Risk Forecast warnings where they are available. Further details of the service can be found at - http://www.sas.org.uk/safer-seas-service/
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The sewage treatment scheme for St Columb Major which provides secondary treatment and ultraviolet disinfection was completed by South West Water in July 1994. Improvements to the inlet works to improve flow handling, and to the storm discharges from the sewage treatment works were also completed at that time. Storm overflow event duration monitoring (EDM) was installed at the St Columb STW, St Mawgan, Trenance Porth, and Mawgan Porth pumping stations by April 2011.
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For the four year (2020-2023) assessment period where data is available, seaweed (macroalgae) was assessed as being sufficient to be objectionable for 5% of visits, with 81% of visits noting the presence of seaweed (macroalgae). This bathing water does not have a history of large amounts of seaweed (macro algae).
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For the four year (2020-2023) assessment period where data is available, phytoplankton (microscopic algae) was not assessed as being sufficient to be objectionable, but was observed as being present on 2% of visits. Phytoplankton (microscopic algae) naturally increase in number at certain times of the year. This process is known as a phytoplankton bloom. This bathing water does not have a history of phytoplankton blooms. The risks to human health from contact, ingestion or inhalation with marine algae that currently occur in UK coastal waters are considered to be low. However, some individuals may be more sensitive and display some reactions. A common marine algae found in UK coastal waters is Phaeocystis, which is often mistaken for sewage as it forms foam and a brown scum, but it is non-toxic.
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This bathing water is subject to short term pollution procedures. The Environment Agency makes a daily pollution risk forecast at this site based on the effects of rain, wind and seasonality on bathing water quality. These factors affect the levels of bacteria that get washed into the sea from livestock, sewage and urban drainage via rivers and streams and how they disperse. When these factors combine to make short term pollution likely we issue a pollution risk warning on this website and the beach manager will display a sign advising against bathing at the bathing water. After a short term pollution event, levels of bacteria typically return to normal after a day or so but it’s possible to have several warning days in a row. Details of the work to reduce the sources of bacteria at this bathing water are detailed in this profile. In 2023 2 pollution risk warnings were issued for this bathing water. All bathing waters have the potential to be affected by a pollution incident and if this occurs a pollution risk warning will be issued with associated advice against bathing on this website.
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2024 Bathing Water Profile for Mawgan Porth
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2024-09-30
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2024-05-01
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Streams and rivers are typically affected by human sewage, animal slurry and runoff from roads. The Menalhyl and Gluvian rivers join at Mawgan Porth and flow across the south of the beach. The Environment Agency have regularly monitored the river at the beach and both rivers have been sampled upstream. We have found that water quality is temporarily worse after heavy rainfall. There is also a very small stream which flows onto the beach at the north.
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There is a STW outfall discharging into the River Menalhyl approximately six and a half kilometres upstream of the bathing water. This discharge is disinfected during the bathing season and designed to protect bathing water quality.
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Environment Agency samplers make observations of litter present on the beach at every visit, this includes assessments of sewage debris, litter and tar. At Mawgan Porth for the four year (2020-2023) assessment period where data is available, sewage debris was not noted at this site. Litter was not assessed as being sufficient to be objectionable, but was observed as being present on 63% of visits. Tarry residue was not noted at this site.
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There are around 30 farms in the catchment, most of which are used for livestock. During and after periods of heavy rainfall, runoff to the Menalhyl River from agricultural land is greatly increased, and the quality of the bathing water can be reduced.
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The catchment surrounding Mawgan Porth is approximately 4,500 hectares. The River Menalhyl rises on the Borlasevath and Retallack Moor Site of Special Scientific Interest (SSSI) and flows for approximately 14 kilometres (km) before entering the sea at Mawgan Porth. The river consists of a main channel which rises to the east of St Columb Major, and the Gluvian tributary which drains the north of the catchment and joins the Menalhyl at Mawgan Porth. The steep catchment means rain runs off rapidly into the river. The catchment is mostly agricultural, with around 30 farms. The rural areas are a patchwork of improved grassland, arable, mixed woodland and heath. The catchment includes the town of St Columb Major as well as St Mawgan and Mawgan Porth and part of RAF St Mawgan.
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Mawgan Porth
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Mawgan Porth
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Sampling point at Mawgan Porth
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184830
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50.46746945104093
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-5.033433876076066
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67470
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Sampling point at Mawgan Porth
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p152 dT23 h59 m59 s
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2024 05 01 t00:00:00
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2024-05-01T00:00:00
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2024 09 30 t23:59:59
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2024-09-30T23:59:59
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2024 32500:1
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Seaweed (macroalgae) and phytoplankton (microscopic algae) are a natural part of the marine and freshwater environment. Below we note whether these have been recorded in quantities sufficient to be a nuisance.
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The majority of sewers in England are “combined sewers” and carry both sewage and surface water from roofs and drains. A storm overflow operates during heavy rainfall when the sewerage system becomes overwhelmed by the amount of surface water. The overflow prevents sewage from backing up pipes and flooding properties and gardens. An emergency overflow will only operate infrequently, for example due to pump failure or blockage in the sewerage system.
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Heavy rain falling on pavements and roads often flows into surface water drains or highway drains, ending up in local rivers and ultimately the sea. The quality of bathing water may be adversely affected as a result of such events.
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It is the Environment Agency role to drive improvement of water quality at bathing waters that are at risk of failing higher standards. It is natural for water to run off the land to the sea. Water quality at a bathing water is dependent upon the type and area of land (the catchment) draining to the water and the activities undertaken in that catchment.
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Discharges from sewage treatment works have improved substantially in England since the 1980s.
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