Here are some other websites that you will find useful:

Lesson Plans:

British Council

Kids against Plastic

Bag It

World Environment Day Afval op School

Environment California

The Story of Stuff

Surf Rider

Less Plastic

Ocean Heroes 

Taking Action:

Greenpeace

Sea Shepherd

The Ocean Cleanup

Captain Planet Foundation

Posters and Artwork:

B Alternative

Thant Myanmar

More information about Zero Waste:

Circuit Zero Dechet