[Airedale1]

Given how close you are to the water; regardless of what town you are in you WILL need permission from NH Department of Environmental Services. That being said, depending upon which town you are in you may also need a variance.

So, you would need to start the ball rolling by filling out a building permit application with an accompanying plot plan. On the plot plan you would draw to scale where the proposed deck would be if it is a change to the footprint of the existing deck.

Also, depending on what town you are in you may also need to pull a demo permit as well in order to remove the existing deck.

As said by others, any experienced contractor in your area should be able to tell you exactly what hoops you will have to jump through to get approved in your specific town.