Wild swimming in the UK has become increasingly popular in recent times.
But reports regarding chemical pollution and poor water quality caused by sewage have also gained prominence.
According to a government assessment released in January 2022, only 14 per cent of England's rivers are categorised as having a "good" ecological quality.
In England and Wales, there were 375,000 documented cases of sewage spilling into rivers and other waterways in that year.
There is another factor which worsens water quality and that is heavy rain.
According to Outdoor Swimmer magazine's Simon Griffiths, “Water quality tends to get worse around heavy rain, since agricultural waste and other pollutants can run off into the surrounding waterways. In addition, heavy rainfall can cause sewer overflows to discharge.”
Water tainted by bacteria found in human or animal faeces can harbour a variety of pathogenic micro-organisms, including viruses, bacteria, and protozoa.
Some of the illnesses associated with wild swimming include norovirus, which can cause vomiting, diarrhoea, and nausea for a few days.
Along with the bacteria E. coli, another major cause of gastrointestinal sickness is the parasite cryptosporidium.
Rashes may also appear.
While these symptoms may disappear on their own, it is not worth taking the risk.
The biggest rule of thumb is to not swim during and right after heavy rainfall.
How long should you wait after heavy rain before swimming
To lower your chance of contracting a recreational water disease, stay out of the water for at least 48 hours following a significant rainstorm event.
However, there is no simple answer or set time as it depends on the site.
How to tell if the water is safe to swim in
There are several apps and maps to guide you to safe waters.
The charity Surfers Against Sewage developed the Safer Seas & Rivers Service app, which notifies users when untreated sewage is dumped into rivers and records the water quality in real time at 370 locations nationwide.
The Rivers Trust also has a handy map showing where the sewerage network discharges treated sewage and overflows of untreated sewage and storm water into rivers in England and Wales last year.
A closer look and a smell of the water you’re entering is usually a good reference point as well. It is best to avoid swimming if your gut detects something is off.
Inland bodies of water, including lakes, rivers, and streams, naturally contain algae. When the correct circumstances are met, a harmful algal bloom may happen. Watch out for blue-green algae, otherwise known as cyanobacteria, as they can produce toxins.
Pets, livestock, and wild animals can all die from these toxins. In addition, they can cause infections if ingested, rashes upon skin contact and in the worst situations, liver damage. It's safest to presume that an algal bloom is harmful because you can't tell by looking at it.
Report anything you think might be blue-green algae to the Environmental Agency in England by calling 0800 807060.
You also probably don’t want to swim in anything that has sewage fungus. This is a whitish-grey bacterial growth on rocks and riverbed.
