This is my "go-to" spot to take friends who have never done standup paddleboarding before - the water is always calm especially by the launching area that is shared by kayakers who rent from Blue Moon Outdoor Center (the rental concession inside the park). The staff there are so friendly and helpful.
I've only used this park for standup paddleboarding and I've never had a bad session since discovering this place last year. You can stay inside the immediate area first to get the paddlers accustomed to the boards...everyone I've taken there for their first time have been able to stand up (woohoo!) with no issues.
Then we go do a full loop going towards the open water, going through a couple of tunnels, "Huck Finn style" and out towards the islands on Biscayne Bay. There are a few quiet coves to explore towards FIU campus. The entire loop takes about 2-3 hours to do...it doesn't feel like you're in Miami as it is so serene. There are lots to see - birds, occasional manatees, fish...all sorts of critters.
I would recommend bringing water or beverage when you're out there as once you're on the bay, you are completely exposed to the sun. There are a few places with tree canopies but for the most part, you are out in the open. It makes for an amazing day on the water.
Oleta has ample parking spaces and clean, well-maintained bathrooms. The park is a very popular spot for bicyclists and kayakers.
They currently charge $6 up to 4 people in a car or $4 for one person on the weekends.
I consider this place my "home standup paddleboard course"! :)