These two reservoirs in Oldham have some nice walking trails to try. It's a beautiful setting with the Upper and Lower reservoirs surrounded by some lovely Pennine scenery.
You can start the walk from the Castleshaw Centre public car park on Waterworks Road, Delph. It's located at the southern tip of the lower reservoir. From here you can pick up paths along the lower reservoir before another footpath takes you around the upper reservoir. It makes for a nice circular walk with good views across the water for the duration of the route.
To extend your walking in the area you can pick up the Pennine Bridleway and further explore Saddleworth Moor and Delph Heights. You could follow the long distance trail north and head to the nearby Dowry and Readycon Dean Reservoirs for example.
The Oldham Way, Crompton Circuit and Rochdale Way also run through the area. They're all good options for reaching several of the other reservoirs dotted around this area of the Pennines. This includes Ogden and Piethorne Reservoirs located just 2.5 miles north west of Cattleshaw.
The reservoir sits on the edge of the Marsden Moor Estate where there are some splendid walking trails.