Lake Clearwater, like Lake Camp is one of the Ashburton Lakes I have had the privilege of visiting a couple of times while I have been living in mid-Canterbury. Lake Clearwater is situated right adjacent to Lake Camp, separated by a small lake-side township. The township has a sleepy, holiday feel to it, with a lot of places crammed in between the two lakes. I have not been in this area in the height of summer, but I can imagine it gets very busy.
Lake Clearwater is the larger of the lakes in the area, with Roundabout being the smallest, then Emma, Camp and finally Clearwater. This lake is much less sheltered than Lake Camp, and is often affected by the prevailing winds. This lake feeds into the Ashburton River, or Hakatere from which the conservation park gets its name.
You can walk a circuit track around this lake which I think would be a really pleasant activity for a slow, holiday afternoon. This is a 10.3 km track so would be good for the fitness, and as it only takes 3 hours you can feel pretty safe that this will be a gentle, easy-going stroll. If you are wanting something a bit more advanced you can make the ascent to the summit of Mt Guy which will give you some nice sweeping views of the Ashburton Lakes, in particular Lake Clearwater. There is a camping ground at Lake Camp and Lake Clearwater you can base yourself at, otherwise I imagine you would be able to rent out a bach in the small township outside of the crazy holiday season.
This is definitely a lake I want to spend a bit more time at, maybe in some of the warmer months as I have only really seen this lake properly in winter.