Over short or long all remnants of human civilisation end in the sea and on beaches. Furthermore there is a multitude of human activities from surfriding to oil drilling which influence the sea and ist creatures.

One way - and much further: 
Garbage in the sea      

Invisible and unhealthy: 
Poison in the sea

Almost suffocated from nitrogen: 
Eutrophication of the Northsea

Exotic litter on the beach

Picture informations:

Author(s) Claudia Mohra
Licence owner Schutzstation Wattenmeer
Licence statement The copyright remains with the author
Licence cc-by-sa 3.0

Industrialisation of the seas: 

They plow and harvest without sowing: 

Free-riders of globalisation: 

The earth suffers from fever:   
Climate change

War games in coastal waters: 
Military activities

Sticky, black and deadly: 

Ducks don’t see the fun in it:   
Water sports

Not only footprints in the sand: 
Tourism on the beach

Further informationen about factors threatening the Waddensea can be found here (in german language):