Dog parks are a great idea in theory, but a possible nightmare in practice. Some things just work that way, Karl Marx wrote a complex book with the same results.
So why is it that I would discourage you from taking your dog(s) to a nice off leash dog park right by the river.
Well first of all the obvious is Disease Transmission. Your dog will come to contact with many other K9s and their feces. Even tho you vaccinated your dog, you don't know if everyone else did and even then, there is many diseases and Insects/Parasites for which you can not even vaccinate or which are hard to control even without contact with other dogs, fleas, lice, etc.
The second reason is a bit more complex and I will try to explain as well as I can.
Dogs and all K9s (wolves, coyotes, etc) are pack animals. They have a very strong pack instinct and pack hierarchy aka "pecking order" for some. This instinct can not really be removed, it can be suppressed and/or controlled to a certain point, but IMO we are working against mother nature and I would rather always work with her as going against nature has not proven very successful yet. In Canada most pet dogs are spayed and neutered which removes a large part of their hormones from their body and therefore some of their natural instincts are not as pronounced, but again we have to remember that we can quite possibly meet a Belgian Malinois female in heat and a German Shepherd intact male at the same park with your lap dog standing between them by accident.
To establish a pack order in each individual pack takes a long time, often several hours or days and even once it is established some of the pack members will continuously challenge it as an instinctual desire to move up in the rank for various reason which is irrelevant for this article. We simply don't have the time to spend at the dog park and new dogs keep coming and going so it is a never ending task which is also very frustrating to your dog because he can never be satisfied with the results and often either give up or can become aggressive simply from frustration. Often even in a healthy and established pack, it can be quite ferocious and bloody when a new mature dog is added to it. Again, esp in unaltered and sexually mature males and females.
The third reason is Training. I keep our dogs fairly or some would say very well trained and dog parks do not really support that idea. Even if your dog is an obedience world champion, you can not control little Daisy that will run full out to your dog and nail him right in his leg as he is healing or sitting beside you. Often then your dog will get in the trouble for no or wrong reason, whether he bites Daisy back or move from your sit because of her and so on. There is simply not much room for success because we don't have control over the rest of the dogs there and even if we did, we might have completely different expectations of what a good or well behaved dog is and what he is supposed to do then Daisy's owner does.
Now some might say "but it is important to socialize your dog". Absolutely it is, but I do it with dogs and people I personally know and trust. That way it is easier to avoid problems, vet bills and it is much better to set your self up for success rather than failure.