I can't help with the sea witch part, but I do want to offer encouragement. Cool! Collect what you can and perhaps you can help others grow that path if there isn't enough for you that already exists. The rune for water is Laguz. It used for a lot of reasons and one is to put yourself or others to sleep if you're having a hard time getting to sleep. Incidently - Kano, the fire rune is great for drawing on your forehead to wake yourself up when you're tired - ie I had to do it twice this morning to get me wide awake so I could drive safely.
Any information you can provide here on what you're interested in with sea witchery or what you want to achieve or do would be appreciated. I think it sounds fascinating. Kelpie I believe are sea witches. I think they have a mischievous side, but then I don't know much about them.