With summer fast approaching and schoolkids breaking for holidays, Paddy Wilson, of Foyle Search and Rescue has urged river users to use “extreme caution” on the waterway.

He said the tragedy that occurred in St Johnston this week was a horrific reminder of how “treacherous” the River Foyle can be. Thirteen year-old Brian McDaid drowned after playing with friends on Foyle sandbanks on Bank Holiday Monday.

Mr Wilson said: “Someone can be standing on a sandbank one minute and believe that they are on solid ground, but the next thing they could find themselves in 20 feet of water. If you were to step off a sandbank you would be straight into the channel.”

There are several areas with “very dangerous” sandbanks along the river, “especially from the Gleneagles area to beyond Culmore Point and from Prehen through to St Johnston and towards Strabane”.

But “unstable” sandbanks are only one of the many dangers posed by the waterway.

Mr Wilson added: “The Foyle is one of the fastest flowing rivers in Europe with very strong currents that can sweep people away very, very quickly. I would appeal to anyone using the river for fishing, kayaking or any other activity to wear life jackets at all times - wearing a life jacket is often the difference between life and death.”

Despite the arrival of summer, the temperature in the river remains low, posing a serious risk to users. With out wet or dry suits, hypothermia can generally set in after three minutes - even the shock of hitting water so cold can stop your heart,” Mr Wilson said.