East Leeds officers said they had already had calls about St Aidan's Nature Reserve and other outdoor spaces in the Leeds area. They added that while they encourage youths to gather outdoors and enjoy themselves, they want them to be as safe as possible. The officers issued this advice on why wild swimming is dangerous: "About 400 people drown every year in the UK, but only a tiny percentage of these drown while outdoor swimming. "An analysis of recent annual accident data shows that of the 12 per cent of drowning victims who died while actually swimming, seven people drowned in swimming pools, 11 in the sea, tidal pools and estuaries, and seven in rivers, lakes, reservoirs or canals. "In addition there were eight who died swimming drunk, 30 who died through ‘jumping in’ to water and 17 who died in ‘jumping and diving accidents’. "95 per cent of all swimming drowning victims were male and many were teenagers." --> READ MORE: Body of 13-year-old boy recovered from River Calder The full warning, posted on social media, said: "Good morning, can we take this opportunity to warn people about swimming in local nature reserves/ outdoor lakes etc. "It's that time of the year again where youths gathering outdoors to enjoy themselves, and whilst we encourage that we want them to be as safe as possible. "We are already getting calls about St Aidan's and other local outdoor spaces. "So far this year there have already been a few cases where people have died whilst swimming outdoors." East Leeds police encouraged people to visit this website for more safety advice. Yorkshire Water has echoed the warning and is also urging visitors to its reservoirs not to be tempted to use water to cool off as the weather gets hotter. Gaynor Craigie, head of land and property at Yorkshire Water, said: “As the weather warms up it is important visitors to our reservoirs are not tempted to get into the water to cool off. "Sadly, we’ve seen recently the dangers water can pose and it is important visitors to our sites understand entering a reservoir can be dangerous. “Low water temperatures can cause cold water shock that may lead to hyperventilation, increased blood pressure, breathing difficulties and ultimately death. Underwater machinery and the currents associated with their operation are also a potential hazard for people choosing to enter the water. “We recently backed the National Fire Chiefs Council’s Be Water Aware campaign and would encourage those visiting our reservoirs to do so safely, which means not entering the water and putting themselves at risk.”