The problem is the nature of the outdoors nature.
If you have a park that's dozens of acres with only a few dozen people. No problem. When you're governor said to go to the parks, that's probably what he was thinking because a lot of parks are like that.
But with almost everyone not working, then that park can be flooded by hundreds if not thousands of people. Social distancing just cannot take place in that situation. That's when local officials shut it down despite the governor's suggestion to go to parks for fresh air.
The same with beaches. They're pretty much design to densely pack people.
The same with aquatic recreation. You may think you're isolated on a boat... until people throw boat parties, or they pull up next to one another and pour a cup of wine and toast. Or they pull up to a restaurants dock where there are other people. On top of that, all those people in the water (whether swimming or in a craft) will eventually require one or more of them being saved by life guards or the coast guard... and that's just more contact with people. There is nothing about aquatic recreation that is *essential*, just like sports venues and gyms are closed, so are waterfronts that attract crowds.
Arguments that start with "surely, they must allow X..." are cut down with a simple counter-question: "Is X *essential*?"
It's time for sacrificing personal luxuries if they cannot be done without drawing people together for a possible virus transmission.
Most states with lockdown orders aren't even letting people congregate even though there may only be five of them and they're all keeping 6 feet apart. "Stay at home" means "stay at home." And "no group gatherings" means "no group gatherings."
With the exception of that which is essential for life and safety.
Depending the state orders, they'll stop you if you're joy riding in your car. Getting in your own boat is no different. Unless perhaps you own the whole lake.
"Stay at home" means "stay at home."
The allowance of local walking presumes being mostly apart from other. When it's seen that that can't actually happen, you're confined to home.