i know orrell water park! i used to fish there every day in the summer holidays when i was a kid, going back about eight years now. was a season ticket holder.
There are two lakes, both about four acre. the top lake has an island and the bottom lake doesnt reall have any features, it used to be reserved for matches only!
Back when i used to fish it, the lake record was a low twenty but the bigest i ever saw was lb17.
Both lakes are full of carp but the top lake has been heavily fished over the years. I would fish the bottom lake if you can, some nice commons and ghosts in there and they will probly be a lot bigger now.
If you go, let me know how it goes, want to go back myself.
Good luck mate