Catan: Seefahrer is an expansion for Catan that includes many water hexes — as well as many different water-hex-heavy variant set-ups — in which players can build shipping lanes, which function similar to roads.
Catan: Seefahrer – 20 Jahre Jubiläums-Edition includes four new scenarios packaged under the title "Die Legende der Seeräuber".
From the publishers site (unofficially translated from German), announced January, 30th 2017:
For 20 years the most popular Catan expansion "Seafarers" adds with a few additional rules endless new possibilities and permutations to play. For the anniversary this May this fascinating expansion will now be released with additional bonus material.
The Anniversery edition includes additionally four new scenarieos: „Legend of the Sea Robbers“. The intense narrative tells, how the sea robbers came to Catan and is connected by an ongoing plot. Therefore, a new way to play is introduced to the CATAN universe.
The scenario expansion „Legend of the Sea Robbers“ will be available as well as a separate box without the content of the Seafarers expansion in selected stores as well as the Catan Shop.