A swimmer sees rain from a unique perspective, as raindrops form balls that race across the surface of a lake, or bounce back, creating small mountains of water where they rebound. Wind can also add to the outdoor experience, creating a wild landscape in the most domestic of swim spots.
But as well as offering different experiences, wind and rain presents different risks. Here’s how to understand more of the changes they make to the water. Swimmers who make themselves aware of the safety issues involved in different conditions can lower their risks. Factors discussed here include pollution, debris and obstructions, currents and flooding, white water, eddies and waves, and cold.
Heavy rain can lead to stronger currents, meaning swimmers need to take extra care, especially in finding safe exit points and not being washed past them. It is generally safer to swim upstream first.
Swooshing down rivers can be fun but you need to know the river well and to check it on the day very carefully. It can be very dangerous after rain because of the fast current and extra debris, and the risk of injured or getting caught in trees or other obstructions increases.
Be especially careful in and around waterfalls, weirs, mill races and pools. Currents and white water can be much faster than usual, and eddies can pull you into faster water. These complex and unpredicable waters are best avoided after heavy rain. Read more on Understanding Weirs and on Waterfalls Risks and Hazards.
Logs, branches, litter, street signs, rocks can be washed down – and any of these and the extra water can change the river from a familiar place to one that is unfamiliar. You can’t always see underwater branches, and being washed against them by a strong current is extremely dangerous as you can be trapped under the water.
River banks can be flooded, meaning exit points you might be familiar with are changed and could be less safe, and this can affect your journey to the water, too. River levels info is available on the Government river levels website and a sea and river levels website
In tidal rivers what is coming downstream in a storm is likely to be met with what is being pushed upstream by the tide, twice a day: run off, debris and pollution can come from both directions. Stronger currents and higher tides will push it on faster but also churn up sediment more.
In 2019 The OSS event team had to cancel the Hurly Burly swim event because of storm conditions. With heavy rains and 30mph+ winds, the Met Office issued a yellow weather warning. There was local disruption: banks were being breached, bridges becoming impassable. Rain was thundering through woodland bringing twigs and debris with it. Flooded rivers, travelling with force and outside their banks, were carrying trees. In the estuary itself, risks increased: Spring tides interacted with the high flow rate to loosen debris that had sat on the banks throughout a long, dry summer.
General advice: Understanding Tidal Rivers and Estuaries
Strong winds can bring a risk of being hit by trees or branches being blown down onto you or into the river or lake, or on the journey there and back. This is more likely when trees are in leaf, especially if it has been rainy as they are heavier and more likely to fall down. There is no easy way to tell which trees might fall down, so be very careful, especially if the winds are force five and above.
Strong winds will cause waves, especially in a lake but also in a river, which needs to be factored in when swimming against it or pushed along by it.
Wind and rain will make it colder both in and out of the water. Think about your clothes – you don’t want them getting wet or blown away, especially when the weather is cold. Assess your own capabilities as well as the place and conditions. See Am I Safe?
Rivers can be affected after heavy rain by pollution: agricultural run-off, discharges from sewage/water recycling plants, and pollution from roads or industry. You can work out from satellite or detailed maps or local knowledge whether there are nearby roads or livestock in fields by the river or drainage channels to it. The locations of and discharges from sewage/water recycling plants are mapped by the Rivers Trust. It is generally best to avoid swimming just downstream of these places after rain, or if you choose to swim keep your head out of water and be very conscious of hygiene after swimming, avoid swallowing the water and be sure to cover up any cuts.
Heavy rain and strong flow can stir up sediment or wash it off fields (especially arable fields) into the rivers directly or via tributaries, streams and drainage ditches. This will make the water cloudy and is classed as pollution.
Flooding can increase the risk of Weil’s disease. See Understanding Weil’s Disease.
There is no need to stop swimming everywhere after it rains: most swimmers can use their senses and judgement and follow the advice in Is It Clean?. There might be sufficient water to dilute any pollution to levels that are unlikely to be unsafe. Heavy rain after a long dry spell is more of a problem.
How long is it necessary to wait after heavy rain before swimming in a river? There is no simple answer or set time, as it depends on the river, and they vary a lot. Generally you can see whether the flow has diminished by the level of the river. In some river spots lower downstream the water can take a while to go down, as it flows into the river off fields, down streams, drainage ditches, and tributaries first, and it depends how flat the land is.
If you feel ill after swimming in open water, especially if it has been raining heavily, consider seeking medical advice and explain that you have been swimming and in what circumstances.
Please note that there is no truth whatsoever in the idea that drinking Coke has any beneficial effects if you are affected by a swim in polluted water.
The latest research from the World Health Organisation concludes there is no evidence of COVID-19 transmission to humans through sewage, but non-infectious traces of the virus can remain in the sewer system, and researchers are using this to study the disease