I have to say...I was disappointed.
I've heard so many good things about Cosmo. Everybody talks about the lake for swimming and the wide open expanses for the dogs to run. They may have left out a few details. But before we get into that...
The set up for the park is nice. There are three different fenced dog runs; 1 is for the lake, 1 is for timid dogs and 1 is for all others.
I don't think that the park has been upkept very well the past couple of monthes. My visit to the lake was, for lack of a better word, disgusting. Huge piles of poop were all along the rocky shore and the water did not look or smell particuarly clean. The shore was made up of rocks and I've been told that there did use to be grass there at one time a little further away from the shore but they've filled that in with rocks as well. I can't imagine that it's particularly easy on the puppy paws.
I definitley did not want my dog swimming in that lake so we moved on to the larger fenced area that had 2 pieces of agility training equipment in it. There's no grass there anymore...it's just compacted dirt. It makes it a little dusty but it serves it's purpose, I guess. There were a few tennis balls here and there and we even found a frisbee at one point. The dog had a great time with that.
The people I encountered at Cosmo seem pretty responsible. Generally everybody maintains responsibility for their dog and cleans up after them.
I have heard rumors of dogs getting sick from being in the lake area so if you're concerned at all it's best just to avoid it.
Unless Cosmo really cleans up it's act a bit I can't imagine I would go here again. There so many superior options for dog parks in the area. If you're looking for one, perhaps try Shawnee Park.
Best of luck!