Understanding Reservoirs

Genuine risks and how to avoid them, myths; campaign for access


Many myths surround reservoirs and the dangers associated with swimming in them. Away from the tower, overflow and any other infrastructure, reservoirs are generally free from hazards associated with rivers and the sea, and without flow, currents or tides.
Factual information about the genuine hazards – and where those are in each case – is vital for public safety. Were signs truthful, more people might comply with them.

Here are the main risks.

Entry and Exit Points:

As for any swim, ensure you can get in and out easily and beware steep banks in reservoirs, especially when you’re cold (remember you lose strength and fine motor coordination with cold incapacitation, even in summer). There might also be sudden changes of depth.

Cold Water:

In summer, the warmer top thermal layer might not be deep, so bear this in mind if you do decide to jump or dive in (with of course the usual provisos about checking the depth and any obstructions first).

As always, swim within your capability.

The layer in which you are most likely to swim will vary in temperature like any other lake, from very cold in winter to over 20° in summer. It is a myth to say that it never gets above 11 or 12°.

Dams and Tower:

There are very real dangers associated with reservoir dams and towers.

The dam has spillways where water is sometimes released to fall to the downstream river, or where a full reservoir overflows. The tower is normally close to the dam, and contains the pipes that take water off for use, whether that’s to be processed for drinking or for hydro-electric power.  There might be a single pipe, or several taking water from different depths. So if you do decide to swim in a reservoir be sure to give those areas a wide berth.

Also be wary of swimming downstream from reservoirs for similar reasons.


Aerators function to mix thermal layers in summer in some reservoirs. We understand they should be marked with buoys. The danger in the area of aerators is a sudden loss of buoyancy caused by the air bubbles in the water. They are best avoided.


There is no reason why we should not have access to swim in reservoirs, with appropriate information on specific risks. However be aware of legalities in your area.

The case for access to swim at reservoirs is shared by OSS campaigner, Owen Hayman, 16 reasons for swimming access in reservoirs, while also dispelling many myths.

Join the Inland Access Group – The Outdoor Swimming Society if you want to push for better access or want advice in negotiating access in your area.

Download The OSS Access Guide to establishing new inland bathing areas, which includes examples where access to reservoirs and other waters has been negotiated by the group.

Words : Lynne Roper, updated
Pictures : See Credits