We are from Chicago and are used to taking our dog to dog beaches when the weather cooperates. Cosmo doesn't have sand on their beach which is good because no worries for the dog carrying it around for weeks afterward but is also bad as it does get a bit muddy on some parts of the shore.
Some people have concerns over potential bacteria in the small water area but I don't see too much need to worry.
The beach area was recently under construction and having the dog jump in off the ledge in the non-dog area (believe this may not be "legal" actually worked a lot better as it led to more swimming due to immediate drop off of water levels with still an easy access in and out.
Definitely recommend this place on hot days where traditional walks/runs/hikes are not possible.