Sunscreen
Use a nontoxic sunscreen. Conventional sunscreens can contain toxins such as oxybenzone (a probable carcinogen that can damage DNA) - these can seep into your skin, and wash off into the sea or lakes where they impact marine life. Luckily, there are mineral-based and organic sunscreens that block rays just as well without the nasty chemicals - so you can get on with playing your eco-part.
Stat: Researchers estimate that about 4,000 to 6,000 metric tons (a little more than a U.S. ton) of sunscreen wash off swimmers annually into oceans worldwide and that sunscreen-induced bleaching threatens up to 10% of coral reefs.
