Logic Masters Deutschland e.V.

Precious Stones in Murky Waters by Patrick Junke

Rules:

Place each of the digits from 1 to 9 in every row and every column.

Two orthogonally adjacent cells have a sum:
- of 3 if there is a Emerald between them (green symbol).
- of 10 if there is a Sapphire between them (blue symbol).
- of 12 if there is a Ruby between them (red symbol).
- of 17 if there is a Diamond between them (white symbol).
- different from 3, 10, 12, and 17 if there is no gem between them.

Cells are either 'river' or 'land'. No 2x2 block can be entirely river or entirely land. All river cells are orthogonally connected.
An arrow indicates a cove, a river cell that is orthogonnaly adjacent to only one other river cell, and is pointing to it. A cell without an arrow cannot be a cove.
Land cells form 'islands' of seven orthogonally connected cells each. Islands do not touch, even diagonally. All islands contain the same set of seven different digits.

Two orthogonally adjacent cells are of opposite types - one is river, the other is land - if they have a Sapphire between them (blue symbol). (All combinations of types are allowed for two orthogonally adjacent cells without a Sapphire between them.)

Negative rules reminder:
- All arrows are given.
- All gem symbols are given.

Here is a link to a SudokuPad version of the grid.