Normal sudoku rules apply. Divide the grid into a number of islands -- orthogonally connected groups of cells. Every island contains a single circled cell; the digit in the circle indicates the number of cells making up the island. The islands are surrounded by a waterway -- a single orthogonally connected group of cells. All caged cells are waterway cells; The digit in a caged cell indicates how many waterway cells are seen orthogonally from that position, including itself (island cells block vision). The waterway cannot form any 2x2 areas.