A 14-year-old boy has died after jumping into the water to a cool off in a "no swimming" area of the River Thames.
The London Fire Brigade (LFB) and the Metropolitan Police searched the Millwall Outer Dock near East Ferry Road following reports of the incident at 6.50pm yesterday.
His body was recovered at about 10.30pm that evening and was later pronounced dead.
The MPS' Detective Superintendent Oliver Richter said: "Our thoughts remain with the family and loved ones of this young boy at this incredibly difficult time.
"As the warm weather continues, I would urge everyone to remember that open water can present serious dangers.
"Please only swim in designated areas and take the time to speak with children and young people about staying safe around water."
The teenager's family has been informed of the tragedy, which is being treated as unexpected but not suspicious.
Police confirmed that inquiries remain underway as officials prepare a report for the coroner.
Meanwhile, London Fire Brigade Assistant Commissioner Patrick Goulbourne added: "Sadly, a teenager has drowned following an incident in Blackwall.
"Firefighters responded to reports of a teenager in the harbour and carried out a full search of the area.
"Despite the best efforts of emergency responders, the teenager was later found dead."
Since Britain started to experience more regular heatwaves, the number of water-related deaths have risen, while authorities scramble to set out health and safety measures.
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Last month, the LFB cautioned Londoners, encouraging city-dwellers to make sure they stayed safe in and around rivers, canals and other bodies of water.
And, back in May, the RNLI issued a water safety warning after a number of water-related fatalities.
The organisation warned: "While the air temperature is warm, the seas are still cold and cold water shock remains a very real risk."
Across the capital, there have been north of 100 "accidental drownings" in the past six years.
