The London Fire Brigade (LFB) has issued a warning for members of the public not to risk their own lives to save their dogs from frozen lakes.
The warning comes after two incidents that occurred this week. A man risked his life to save a stranger's dog in Victoria Park on Monday.
And on Wednesday, a woman was spotted jumping into a frozen boating lake in Alexandra Palace to rescue her dog, which had been running across the ice chasing birds.
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According to the Standard, the woman took off her coat and shoes and dived into the water with a life ring. She directed her dog to the side of the lake, where someone helped them out.
The LFB warned this is not something anyone should do.
A London Fire Brigade statement read: "As the capital is hit with frozen fog, we're warning people to stay at a safe distance away from ice and frozen ponds.
"If people fall into an icy lake, the risk of hypothermia is very high and people won't survive for very long.
"Parents should talk to their children about the dangers of going on the ice, as it may look sturdy enough to stand on but it often isn't, can be of variable thickness across the same stretch of water and can therefore easily break when people stand on it.
"This warning is especially relevant to dog owners. We strongly recommend that all dogs are kept on a lead so that they don't run off and end up in difficulty.
"Firefighters are trained and have specialist equipment in case anyone does get stuck on, or in, an icy lake or pond.
"This includes using emergency rescue boats, inflatable rescue paths, mud lances, thermal clothing and dry suits.
"Stay off any frozen pond, lake or canal."
London Fire Brigade Community Safety Group Manager Mark Hazelton said it's important to think about the risk posed by icy ponds, lakes and canals and take appropriate precautions. He explained: "As soon as ponds and lakes freeze over we know there is a risk that people may make the mistake of walking on and falling through the ice.
"Some people take astonishing risks, especially pet owners whose dogs have gone onto the ice and young people who seem unaware of the dangers.
"Please, for your own safety, stay off of any frozen pond, lake or canal as there is a high risk it wont take your weight and when it's cold, hypothermia sets in rapidly and can prove fatal.
"If your dog or any other animal ends up on the ice, stay put and call 999 so firefighters can rescue it, rather than taking risks yourself."