To spend time on the water, of course, you need a kind of watercraft. Our favorite is the SUP (Paddle Board), but others may prefer to use the canoe or kayak. In our comments, we will refer to the SUP, but everything is 1: 1 for other water sports.(Of course, you need a paddle next to your board.) Sounds logical, but believe us, it's on the checklist!)
You do not even have to own equipment, you can rent boards and boats in many places and only in rare cases our furry friend is not welcome. To be sure, you should still call and ask before.
If you are considering buying a board, consult with a specialist and ask explicitly about the options of bringing a dog with you. But the board should have a little bit more stability, because your dog will cause a little swell when he moves on the board. So the board in front of the stand should have a little volume and a certain width. Touring and all-round boards are ideal, but wave or even race boards are less suitable. It does not matter if you buy an inflatable SUP, an iSUP, or a hardboard. We would always recommend a hardboard because of higher security, stability and deployment viability, but we are also nerds.
As Touringboard we can recommend the CIRCUS Liberty. It is 30 inches wide enough and stable to tilt and has 280 liters volume enough payload for your dog and additional equipment. Another advantage is the second luggage net at the stern, where you can stow things for you.