The ponds are one of the glories of Hampstead Heath. They were created for a number of reasons, but the bigger ones were originally dug out as reservoirs for London's water supply in the 17th and 18th centuries. There are over 30 ponds on the Heath, but there are six major ones, in two different valleys, one of them in the valley of the River Fleet, here a very small stream.
Three of them are used for bathing, one mixed, one for the ladies, and one for the men. Here we see the mixed bathing pond, on an idyllic summers day, with a couple of swimmers on the swimming stages at the far end.
The
ponds are not just for swimmers. Here we see some of the fishers too,
who spend the summer, fishing from the dam at the far end. 
Here
is the men's pond, which is the biggest pond of all. On the right is the
jetty from which it is possible to dive in, with the changing rooms hidden
in the trees. It is a delightful place to swim in the summer. 
And
here is a more dramatic view of the men's pond, looking into the sun,
and with the ubiquitous fishers in the foreground.
And
here is the boating pond. It is very shallow - only a couple of feet in
most places, and here it is possible to sail model boats and toy yachts.