Images #276 and #278 I think may be very early 60's maybe late 50's. There is now a concrete bank around the lower lake, that's always been there since I was a kid. I have a feeling that when they reinforced the banks of the lower lake, they also reduced the depth too. you can see the new bank in #277.
The lakes were drained about once a year or so. I have certainly seen them drained a couple of times. In the upper lake there was always a build up of silt to left of the incoming brook. It would interfere with the model yacht club activity's that my dad was a member of, so they would drain it and dig it out.