Understanding Tidal Rivers and Estuaries

Tidal swimming risks and hazards

Tim Bridges

Swimming in tidal waters can be fun if you do your research and follow advice on swimming safely outdoors generally, in rivers and the sea, and especially in tidal rivers and estuaries. And find out about the specific river, ideally from locals who know it well.

Main hazards


  • currents and eddies – which can be faster than you expect, and not always obvious
  • flotsam and jetsam, hidden obstacles
  • effects of the weather
  • health risks and pollution
  • boats and other river users


  • tides and rip tides
  • unpredictability
  • impact of wind
  • boats­

Tidal rivers and estuaries – all the above plus

  • silty or muddy water
  • long gaps between access points
  • very muddy exit points
  • brackish water
  • changing flow direction
  • tides and bores
  • rules applying to navigable waters

There are some advantages

  • you can use the speed of the tide or bore to help you swim a distance faster
  • the water can be warmer, as water flows over extensive mudflats


Slack tide in Suffolk river Imogen Radford

Understanding the hazards in tidal rivers and estuaries

  • Be aware of all hazards and to understand them, and – very importantly – know the local water and how it behaves. It’s best to tap into local knowledge and to observe the water. Talk to sailors, boaters, canoeists and kayakers, anglers and experienced swimmers.
  • Learn to read tide tables and sea charts and to understand them. In some places it is best to swim in the slack water either side of high tide, in other places at low tide. Tides are quite complicated, in terms of times, directions and speed. The local tide table might not apply exactly to the place you might be thinking of swimming, and the tide does not always come at the time predicted.
  • Be aware of boats, keep away from them, and make sure they can see you, with a bright swim hat and tow float. Be aware of the rules of navigation, but adapt to the particular circumstances. Some boaters are inexperienced and can be unpredictable. The ladders at mooring points should only be used with great caution, and not if boats are around, as boats can approach at speed.
  • Check for sources of pollution. Heavy rainfall can have an impact on water quality. Areas busy with boats can be polluted by fuel or waste spills or discharges.
  • Heavy rain can mean flooding, faster flowing water, and debris. Be very cautious.
  • Swimming is banned or only allowed with special permission in some tidal rivers, such as the Thames below Putney Bridge.
Swimmer with tow float, swimmers entering muddy tidal river Imogen Radford

More detailed advice

Outdoor Swimming Society advice on rivers, currents and eddies, tides, rip currents, waves, coastal weather, and sea kayakers’ advice on currents.

Outdoor Swimming Society: understanding rivers

Outdoor Swimming Society: currents and eddies

Outdoor Swimming Society: tides

Outdoor Swimming Society: understanding rip currents

Outdoor Swimming Society: understanding waves

Outdoor Swimming Society: coastal weather

Sea kayaker advice on currents


Words and photographs Imogen Radford


Waves as tide turns in urban river, buildings on shore, swans on water's edge Imogen Radford