Puzzle 216: Matryoshka Nurikabe

Rules: The challenge is to paint each cell black or white, subject to the following rules:

1. Each numbered cell is a wall cell, the number in it is the number of cells in that wall.
2. Each wall must contain exactly one numbered cell.
3. There must be only one stream, which is not allowed to contain "pools", i.e. 2x2 areas of black cells.
4. All centre squares, starting with the 2x2 square and working outwards produce gradually larger Nurikabes of their own.