It’s surprisingly difficult to uncover the truth about dangers associated with reservoirs. Because many people who are opportunistic occasional swimmers will go to swim in reservoirs on a hot day, the OSS believes that 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.
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.
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).
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 sneak a cheeky dip in a reservoir it makes sense 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.
There are reservoirs where people swim officially, but if yours is not one of these you might wish to contact the OSS Inland Access group with a view to negotiating swimming there. In the mean time, be wary of both legality and hazards. As always, swim within your capability.
We’d be very happy to hear from anyone who understands more about the potential hazards associated with reservoirs.