Grüner Brink, Protected area on Fehmarn's north coast, Germany.

Grüner Brink is a 134-hectare nature reserve on Fehmarn's north coast, a strip of land 2.5 km long and up to 180 m wide between an 1872 dike and the Baltic Sea. Behind the dike lie small, slowly silting beach lagoons, cut off from the open sea by barrier spits and flooded with salt water only during strong storm surges.

The area formed through natural processes following a severe flood disaster in 1872 that prompted construction of a protective dike. This embankment permanently altered ocean currents in the region and allowed the development of barrier spits that now define the landscape.

The reserve's birdlife is what draws most visitors: up to 170 species are counted over a year, and the shallow beach lakes serve as breeding grounds for rare water birds. The eastern section borders a bathing beach and a kite-surfing area, so birdwatchers and beachgoers share the same stretch of coast.

The reserve is a 2.5 km long, up to 180 m wide strip between the dike and the Baltic Sea; the beach and kite-surfing area lie to the east. Salt water reaches the lagoons only during strong high water, so the inland lakes stay largely cut off. Stay on the paths to avoid disturbing breeding waterbirds.

The dike built after the 1872 flood created the reserve itself: changed currents deposited sand that closed off small lagoons, which are now silting up. Salt water enters these beach lakes only during strong storm surges.