Here's an interesting article on the damage sunscreen, of all things, does to our reefs!
Who knew?

Sunscreens are among the products we are encouraged to use liberally to protect ourselves from
the sun’s harmful rays. However, researchers are finding that while protecting humans, some
compounds in many sunscreens can harm the coral on our reefs. Researchers testing the effects
of sunscreen on corals explain that chemicals in sunscreen can awaken coral viruses. The coral
then becomes sick and expel their life-giving algae. Without these algae, the coral “bleaches”
(turns white), and often dies.

We may not realize that the products covering our skin wash off when we enter the water, and
it adds up! Research tells us that 4,000 to 6,000 TONS of sunscreen enters reef areas annually.
This does not spread out rapidly or evenly over the entire ocean, but concentrates on popular
tourist sites. It is estimated that 90% of snorkeling/diving tourists are concentrated on 10% of the
world’s reefs. This means that our most popular reefs, such as those in our national parks, are
exposed to the majority of sunscreens.

Sunscreens: The double edged sword
As a visitor to the park and the reefs, you can reduce the risk of harming coral by taking a more
“reef friendly” approach to sun protection.
CHECK THE LABELS: While no sunscreen has been proven to be completely ‘reef-friendly,’
those with titanium oxide or zinc oxide, which are natural mineral ingredients, have not been
found harmful to corals. Sunscreens sold for children or for those with sensitive skin may contain
these gentler compounds as the active ingredients.
COVER UP: You can protect yourself as well as the reef by ‘covering-up’ before you enter the
water. On the water, wear hats, sunglasses and light, long-sleeved clothing to protect you.
In the water, a long-sleeved shirt or rash guard will help prevent sunburn.
Remember, if it’s on your skin, it’s on the reef. Be reef friendly!
Reduce the amount of sunscreen you leave behind…

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Here's the link.