Locks, gates and bridges: the man-made river hazards

Rivers and canals are full of things people have built: locks, sluice gates, weirs and bridges. They're part of what makes a waterway interesting to swim along, and they change how the water behaves around them. This guide covers what the people who run UK waterways say about swimming near them.

Questions to ask before you swim

Ask, too, whether you'll be swimming under any bridges. Weirs are a different matter: don't swim near one. They get their own guide.

Bridges: what's underneath, and what's coming

A bridge looks harmless from the water. The hazards are the things you can't see, and the things heading your way.

The Environment Agency lists bridges, along with locks and flood channels, as places where water can hide hazards. It has warned about young people jumping from bridges into rivers, and its advice is not to jump or dive into the water at all, because the depth can vary and there can be hazards out of sight. In one Environment Agency campaign, the local fire and rescue service listed shopping trolleys, scrap metal and wooden splinters among the things that could cause serious injury. The Canal & River Trust says jumping into rivers or canals from bridges is extremely risky: canals can be shallow, and you won't be able to see the depth or any obstacles in the water.

Then there's the current. The Outdoor Swimming Society (OSS) points out that if you can't swim upstream against the flow, you won't be able to get out of the way of things downstream, and it names bridges and trees. It also warns about features that can trap and hold a swimmer underwater.

On a navigable river there's boat traffic too. The Environment Agency notes that people on larger boats can find it very hard to see swimmers, and the OSS says to make sure you're visible and know the river's rules.

Locks: off limits in most places

On the canal network, the rule is clear. The Canal & River Trust's byelaws don't permit swimming in its canals. The Trust describes them as working spaces with moving boats, weirs, sluices and locks, which it says makes them unsuitable and unsafe for swimming. Any swim that doesn't take place with a licensed club is unauthorised, though the Trust has identified some inland waters that may suit supervised swimming. On water quality it is just as direct: "We don't test our water, but we know it is not of swimming quality."

In England, the Environment Agency manages locks, weirs, sluices and pumping stations on many rivers. It has said jumping or diving from them is strictly prohibited, and that people who ignore the warning signs could be committing an offence. Its advice is to read the information boards around locks and always pay attention to warning signs.

Why locks are so dangerous

The Canal & River Trust says locks are a lot deeper than people expect, and that they have hidden underwater shelves, called cills, which can seriously injure someone. The Environment Agency adds that water levels can change quickly as lock gates open and close, creating strong flows and turbulence, and that boats may come in and out unexpectedly, which raises the risk of collision or injury for anyone in the water.

In a lock you can't see the bottom, can't predict the water and can't count on being seen. The water is cold, too: the Canal & River Trust notes that even on a hot day it can be extremely cold, so read up on cold water shock before you go.

Gates and sluices

Sluices are gates that open and close to let water through. The Environment Agency warns that sluices can open and close automatically without warning, releasing sudden surges of water that can quickly overwhelm even strong swimmers. Its general advice is not to go in near weirs, locks, pipes and sluices, which are often linked with strong currents, and to stay well clear of these structures.

Before you swim near any of them

• Check the rules. The Canal & River Trust's byelaws don't permit swimming in its canals, and signs at locks and weirs carry the local warnings.
• Look at the river. After rain, flows are higher and faster, so read river swimming after rain first.
• Plan your route so the current can't carry you onto a structure, and swim upstream first where you can.
• Make yourself visible to boats.
• Know who to call. In the UK, call 999 or 112; inland, ask for the fire service. Our guide to who to call if it goes wrong has the detail.

For everything else about a river swim, from reading the current to finding your way out, see the river swimming guide.

Sources

1. Canal & River Trust, Open water swimming FAQs
2. Canal & River Trust, Open Water Swimming
3. Canal & River Trust, Summer holiday sunshine prompts us to ask you to stay out of the water
4. Canal & River Trust, We are asking teenagers to stay out of the water this half term
5. Environment Agency, Helping you choose where and when to swim in open water
6. Environment Agency, Environment Agency and partners warn Berkshire river users to stay safe in heatwave
7. Environment Agency, Stay safe around rivers: warning as lockdown eased and temperatures soar
8. Environment Agency, Be aware of safety warning signs when swimming near water structures this summer
9. Outdoor Swimming Society, Understanding Currents And Eddies
10. Outdoor Swimming Society, Understanding Rivers

This guide is general information, not a substitute for local knowledge or training. Conditions change: check them on the day, and if in doubt, don't go in. Images on the blog are illustrations, not pictures of specific spots.