Six Islands

Sudoku rules (sort of) apply -- No row, column, or box contains the same digit more than once.

There are six islands (orthogonally connected regions) each containing the digits 1-6 with no repeats. Each of the given digits belong to a different island from the others.

The islands are separated by a single, orthogonally connected waterway. Note that islands do not touch diagonally, and that the waterway does not contain any 2x2 area. All water cells are EMPTY (contain no digits).

Circled digits (all land cells) indicate exactly how many adjacent cells (up to 8) contain water, and ALL such cells are indicated; that is, non-circled digits will NEVER have that number of adjacent water cells.

The clues outside the grid indicate the sum of island cells along the indicated diagonals.