Five minutes east of Kumara heading towards Arthurs Pass is the Kapitea Reservior, also known as Dillman's Dam. On a day without wind the reflections are breath-taking.
It's a great spot for walks, photography, kayaking and if eels don't frighten you, it would be ideal for swimming too.
This area is owned by DOC. Camping is welcomed as long as your camper van or motorhome/bus is self contained. However no freedom camping is allowed. I wish I'd taken a photo of the area where you can camp, it's right beside the water with awesome views. A new toilet block has been built in the picnic area too.
Be careful if you're thinking of visiting with pets, we noticed several signs stating 1080 had been dropped in the area.