IMO I think it may well be the spot, but as someone pointe dout earlier, AA used to be a quarry. Whether it was a reservoir before this time remains to be seen.
It is my understanding there has been an area of water here for some time. Open-cast coal mining (technically this is quarrying, but for coal!) has completely changed the landscape to the east and south of the park, so it is very difficult to tell how it used to be. As the land was part of the Shipley Hall estate a lake is likely as a standard feature of a large estate, a status symbol if you like!
I recall a reference to the lake being made bigger after mining somewhere but I can't think where. Also, somewhere I have seen a map from the 70s which definately shows water here, It might be at my dad's, I'll check next time I go.
The bridges at the bottom of the lake are very old and obviously crossed water courses. The abutments where you now go into the park took the same roadway over a railway line, the Great Northern Railway branch to Heanor (from Ilkeston). This would have seperated a then slightly smaller lake from the Woodside colliery sidings on the other side, probably at a higher level. The course of the railway north of the park is still shown on maps, I keep promising myself that one day I will have to investigate the area!
A quick search found this page: http://www.canals.btinternet.co.uk/canals/nutbrook.htm
and from it:
"Shipley Hall used to stand on the land over to the west. The hall itself was demolished long ago and the estate was taken over by the NCB. However, the land is now part of Shipley Country Park and the remains of the hall are open to the public. There are two large stretches of water in the this area, both of which once supplied the canal. To the west is Mapperley Reservoir while to the east is Shipley Lake. The latter is now within the grounds of the American Adventure theme park. "
Good luck with the photos Sarah, this could get interesting!
Edit: Definately water there in 1887. From http://www.old-maps.co.uk/
(it's like an olde worlde multimap!!): http://www.old-maps.co.uk/oldmaps/index ... untyCode=8
Select the Derbyshire option given. Interestingly this map shows very little coliery development. The big blacked out area appears on the Nottinghamshire map, as the county boundary would have been different back then.