Visitors to a park are being advised not to cool off by swimming in the rivers and lakes in the hot weather.
Rangers from Lee Valley Regional Park, which stretches from Watham Abbey to Lower Nazeing, said they had to ask a number of people to leave the park after they were caught swimming.
The 10,000 acre park hosted the canoe slalom event at the London 2012 Olympics.
Visitors are also advised of the hazards of using boats and inflatables such as dinghy’s and lilos in the water and to keep their pets under control.
Health and Safety Officer at Lee Valley Regional Park Authority, Andy Waters said: “With the recent heatwave and now with schools breaking up for the summer, we’re seeing more and more people swimming and boating in waters such as Glen Faba, Bowyers Water and the North Met Pit.
“The dangers of swimming in waters such as these have been highlighted over recent weeks in the media with a number of drownings reported.
“Many of our waters used to be gravel pits and people underestimate how dangerous they can be, with shallow shelves dropping without notice into very deep water, underwater obstructions from the original gravel abstraction and thick aquatic vegetation as part of the natural environment.
“The water may also feel relatively warm on the surface, but just a few feet below can be icy cold even in the hot weather and can very quickly cause severe cramp and hypothermia.
“It is far safer to swim in purpose built and supervised swimming pools, take boat trips from the boat centre in Broxbourne or go kayaking at Lee Valley White Water Centre.”