Firefighters rescued two children from the River Colne in West Drayton.
The Brigade's fire and rescue unit crews used water rescue equipment to assist an 11 year-old boy and a 15 year-old boy from the water. Both boys were taken to hospital by London Ambulance Service. One further adult man exited the water before the Brigade arrived and declined medical treatment.
A London Fire Brigade spokesperson said: “The best thing you can do if you see someone in difficulty in the water is to call 999, try to give an exact location about where you are and keep your eyes on the last spot you saw them.
"If you go into the water to rescue people, pets or belongings, you could be putting yourself at risk as well.”
The Brigade was called at 1839 and the incident was over for firefighters at 2038. Two fire engines from Heathrow and Hayes fire station and fire and rescue units from Wembley, Bethnal Green and surrounding fire stations attended the scene.