The Bark Park isn't very large, about the same size as Ackerman dog park. It's fairly wide open though and offers a lot of room for dogs to run around. Benches provide plenty of places for people to sit, and several trees provide shady spots during hot weather.
The small dog area is a long narrow strip adjacent to the main dog park. There were no small dogs around when I was there, so I'm not sure how often it gets used. Looks like it would be a good place for people with smaller dogs that don't want to risk them getting bowled over by bigger dogs. Most of the small dogs I've seen though play just fine with big dogs.
There's no water fountain installed in the dog park, but a large bucket in each area provides water. The water comes from a hose running from the Rec center to the dog park. Filling the bucket requires walking out of the dog park over to the building to turn the water on.
There are a few sandy areas where dogs can plop down to relax, cool down or work out some of their digging urges.
A Google Map to the IOP Bark Park.