Swimming is a great cardio work out.
Yeah it  will decrease your stress also 
In fact, swimming in the ocean might actually help improve health and mood even further than in other bodies of water thanks to all the extra vitamins, minerals, and trace elements found in the ocean not found elsewhere.
You can try this  in morning . it  will make your  day for  sure. 
It's advised to eat 2-3 hours before exercise and swimming to allow their stomach to empty, so make sure not to eat breakfast right before swimming.
Yeah  you are exactly right  for this advice  
You must be a strong swimmer to swim in the ocean. Ocean swimming is definitely more challenging than in other waters.
yeah  i am agree with you 
I am glad you agree. What oceans do you normally swim in?
I suggest  you try to do it  in morning ocean .