The good people at Google Street View have recently partnered with The Catlin Seaview Survey to provide underwater street views of several breathtaking reefs around the world.
You can take your students on a fieldtrip to swim with sea turtles and manta rays without having to be scuba-certified. From identifying the variety of aquatic life forms depicted in and around the reefs to writing short stories set in the reefs; the possibilities for classroom use are as wide as the ocean and as deep as the sea.
You can explore the complete collection here.