Ocean magic is considered to be the highest and most powerful type of magic. It is however difficult to work with, due to it's being a type of Chaos Magic. Typically you would add ocean water to any spell which you want to "energize" or make "more powerful". Same holds true of ocean (not lake) beach sand. Atlantic Ocean water is considered the most powerful of all, with that of the highest energy vibrations coming from Maine, Nova Scotia, Wales, or Scotland. Spells cast on the beach during a sea storm (hurricane) are said to be the most powerful of all.
Let's take a second to think about the ocean. It can destroy villages, create storms that decimate cities, and it is the place where most of life on Earth is. It is held very high in nearly all in most religions. It is one of the main elements with an entire cardinal direction unto itself. There are many spirits associated with it for example sirens and undines. It is very potent to say the least.
Recently i have been dealing with the ocean because i have been on vacation. I have found that the ocean is full of power but it is difficult to use since the ocean is so unpredictable. All forces of nature have much power but asking the ocean to help you, at least in my experience is difficult because it is always changing and is not eager to help you.