We used to go up in July or August. Park at Summit lake and hike down and camp for a couple of days. That or hike up from Idaho Springs Res, about 6-7 miles. Either way, long hike but the trout fishing was always good, that's all we ate while camping there. Probably still snowed in this time of year, just look up at Mt. Evans and see what it looks like. There are a couple of other lakes a couple of miles north around the ridge from the lower lake. Never been to those but always wanted to try them. Check a topo map and you'll see them.
I think they are the colorado river strain, but it is hard for me to tell the exact sub-species. I believe the population is helped out by periodic stocking by plane or horse, but they reproduce naturally as well.
I have seen people camping but no specified sites are built in. The lower lake would probably be best to camp overnight - it is just above treeline with the upper lake (fishes good too) in a deep bowl with not much place to go to get out of the bad weather you can expect to enjoy periodically
We used to pack in and camp between the two lakes. Nice little waterfall between the two and a few trees. Don't take much more than the bare essentials and a two man tent or you'll get tired real quick! We would take very little food and eat the fish we caught mainly and boil water to drink to keep weight in the packs down. Definately roughing it!!