Sailors for the Sea Powered by Oceana is the leading ocean conservation organization that engages, educates and activates the sailing and boating community toward restoring ocean health.
https://www.sailorsforthesea.org/
Their Green Boating Guide gives lots of great tips on how to help keep the ocean clean while you sail.
https://www.sailorsforthesea.org/programs/green-boating-guide
Their KELP program (Kids Environmental Lesson Plans) has more than 50, free, downloadable activities that address topics including overfishing, climate change, ocean acidification and plastic pollution.
https://www.sailorsforthesea.org/programs/kelp