Can you go swimming in the intercoastal part of the park?

Yes they have a great area called Whiskey Creek that offers Canoe and kayak rentals

Ive swam in whiskey creek it is nice, cool, and clear water. You may see blue crabs and baby baracuda but no harm they run away from you anyway.

No swimming in intercoastal part. Just kayaking, boating and paddle boarding. But I bet you can get away with falling off your board for a quick dip.

Also, if you have your own kayak, once you cross over into the park you can park your car, bring your kayak to where the intercostal starts and go in right there.

Large container ships transit there all day