Yeah all "non-essential" businesses are shut down across the state. Here's more info and what is considered essential:
Gas stations are listed under essential, which is probably why marinas with gas can remain open, but from what J_R posted sounds like it excludes recreational use.
Also exempt are single employee businesses. So if you know of any marinas that can function with no more than one on-site employee at any given time I guess they could remain open. But I'm sure they will be bombarded due to the closure of other larger marinas. And I'm betting there will be a massive line of boats waiting to launch/unload at the unmanned boat ramps.
But another issue... I went to get trout worms today and realized all the bait shops are shut down too... So what are we going to do about bloodworms? Guess if everyone has sabikis from last year they can jig up herring. But no bait and it won't matter if the marinas are open.