For Christians, doves of peace, Angels, and the Serenity prayer all represent inner peace and bliss. see also - http://www.e-Serenity.com/
A lake can represent serenity.
If you are referring to the woven square knot that has 4 parts sometimes called a quadrequetta, this represents the 4 Gospels from the Bible and is found in "The Book of Kells" in many of it's...