Porthoustack is on the south coast of Cornwall. It is a remote pebble beach, approximately
240 metres wide, backed by cliffs. There is a stream flowing across the beach to the
sea.
The South West Water sewage treatment scheme for St Keverne, which provides secondary
treatment, was completed in early 1972. Storm overflow event duration monitoring (EDM)
was installed at St Keverne STW by April 2011.
For the four year (2020-2023) assessment period where data is available, seaweed (macroalgae)
was assessed as being sufficient to be objectionable for 11% of visits, with 79% of
visits noting the presence of seaweed (macroalgae). The bathing water can become covered
with large amounts of seaweed, depending on tides and the weather. This bathing water
does not have a history of large amounts of seaweed, but it can be noticeable from
time to time.
For the four year (2020-2023) assessment period where data is available, phytoplankton
(microscopic algae) was not noted at this site. 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.
There are no active pollution risk forecasts made at this bathing water. However any
bathing water has the potential to be affected by a pollution incident and if this
occurs a pollution risk warning with associated advice against bathing will be issued
on this website.
Streams and rivers are typically affected by human sewage, animal slurry and runoff
from roads. The St Keverne Stream flows onto this beach. The Environment Agency have
monitored the stream between 1986 and 2008, and found that water quality is temporarily
worse during and after heavy rainfall.
The outfall from St Keverne STW discharges to the St Keverne Stream 1.8km upstream
of the bathing water. This discharge is designed to protect bathing water quality.
Environment Agency samplers make observations of litter present on the beach at every
visit, this includes assessments of sewage debris, litter and tar. At Porthoustock
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 47% of visits. Tarry residue was not noted at
this site.
There are approximately 10 farms in the catchment. During and after periods of heavy
rainfall, runoff to the St Keverne Stream from agricultural areas is greatly increased,
and the quality of the bathing water may be reduced.
There is a private surface water outfall near the bathing water. If any concerns arise,
the Environment Agency will investigate and request immediate remedial action from
those responsible.
The catchment surrounding Porthoustock is approximately 295 hectares. The St Keverne
Stream is approximately three kilometres (km) long and flows from the hamlet of Treskewes
to the beach. This is a gently sloping coastal catchment which becomes steeper at
the beach. The steep slopes in the lower catchment mean rain runs off rapidly into
the stream.
Land use is agricultural, with around 10 farms, a mixture of improved grassland and
arable, and some woodland. The catchment includes the village of St Keverne and is
located in the Cornwall Area of Outstanding Natural Beauty (AONB). The top of the
catchment is in the Lizard Special Area of Conservation (SAC) and East Lizard Heathlands
Site of Special Scientific Interest (SSSI).
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.
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.
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.
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.
